diff --git a/assets/js/admin/products-admin.js b/assets/js/admin/products-admin.js
index 5ed037916..7cf1de715 100644
--- a/assets/js/admin/products-admin.js
+++ b/assets/js/admin/products-admin.js
@@ -825,6 +825,14 @@ jQuery( document ).ready( function( $ ) {
 			const removedIds = attachmentIds.filter(id => !selectedAttachmentIds.includes(id));
 			const newIds = selectedAttachmentIds.filter(id => !attachmentIds.includes(id));
 
+			// Check if the selection exceeds the Facebook image limit
+			const maxImages = window.facebook_for_woocommerce_products_admin && window.facebook_for_woocommerce_products_admin.max_facebook_images ? 
+				parseInt(window.facebook_for_woocommerce_products_admin.max_facebook_images) : 21;
+			if (selectedAttachmentIds.length > maxImages) {
+				alert(`You can only select a maximum of ${maxImages} images for Facebook catalog sync. Please reduce your selection.`);
+				return;
+			}
+
 			// Remove unselected image thumbnails
 			$container.find('.form-field').each(function () {
 				const $imageThumbnail = $(this);
@@ -890,6 +898,37 @@ jQuery( document ).ready( function( $ ) {
 					attachment.fetch();
 					selection.add(attachment ? [attachment] : []);
 				});
+
+			// Add real-time selection limit enforcement
+			const maxImages = window.facebook_for_woocommerce_products_admin && window.facebook_for_woocommerce_products_admin.max_facebook_images ? 
+				parseInt(window.facebook_for_woocommerce_products_admin.max_facebook_images) : 21;
+
+			let isValidating = false;
+			let lastAlertTime = 0;
+			
+			selection.on('add', function(model) {
+				if (isValidating) return; // Prevent infinite loop
+				
+				if (selection.length > maxImages) {
+					isValidating = true;
+					selection.remove(model);
+					
+					// Only show alert once every 2 seconds to prevent spam
+					const now = Date.now();
+					if (now - lastAlertTime > 2000) {
+						lastAlertTime = now;
+						// Use setTimeout to prevent blocking and allow DOM to update
+						setTimeout(function() {
+							alert(`You can only select a maximum of ${maxImages} images for Facebook catalog sync.`);
+						}, 10);
+					}
+					
+					// Reset validation flag after a short delay
+					setTimeout(function() {
+						isValidating = false;
+					}, 100);
+				}
+			});
 			});
 
 			// Handle selection of media
diff --git a/includes/Admin.php b/includes/Admin.php
index 852c49c61..b8518f888 100644
--- a/includes/Admin.php
+++ b/includes/Admin.php
@@ -25,6 +25,9 @@
  */
 class Admin {
 
+	/** @var int maximum number of images allowed for Facebook catalog sync */
+	const MAX_FACEBOOK_IMAGES = 21;
+
 	/** @var string the "sync and show" sync mode slug */
 	const SYNC_MODE_SYNC_AND_SHOW = 'sync_and_show';
 
@@ -195,6 +198,7 @@ public function enqueue_scripts() {
 						'product_not_ready_modal_message' => $this->get_product_not_ready_modal_message(),
 						'product_not_ready_modal_buttons' => $this->get_product_not_ready_modal_buttons(),
 						'product_removed_from_sync_field_id' => '#' . \WC_Facebook_Product::FB_REMOVE_FROM_SYNC,
+						'max_facebook_images'             => self::MAX_FACEBOOK_IMAGES,
 						'i18n'                            => [
 							'missing_google_product_category_message' => __( 'Please enter a Google product category and at least one sub-category to sell this product on Instagram.', 'facebook-for-woocommerce' ),
 						],
@@ -1610,14 +1614,34 @@ private function process_variation_post_data( $index ) {
 		$image_url    = isset( $_POST[ $posted_param ][ $index ] ) ? esc_url_raw( wp_unslash( $_POST[ $posted_param ][ $index ] ) ) : null;
 		$posted_param = 'variable_' . \WC_Facebook_Product::FB_PRODUCT_VIDEO;
 		// phpcs:ignore WordPress.Security.NonceVerification.Missing -- Nonce verification is handled in save_product_variation_edit_fields method
-		$video_urls   = isset( $_POST[ $posted_param ][ $index ] ) ? esc_url_raw( wp_unslash( $_POST[ $posted_param ][ $index ] ) ) : [];
+		$video_urls = isset( $_POST[ $posted_param ][ $index ] ) ? esc_url_raw( wp_unslash( $_POST[ $posted_param ][ $index ] ) ) : [];
 		// Fix: Look for the actual POST key format that WooCommerce generates
 		$posted_param = 'variable_' . \WC_Facebook_Product::FB_PRODUCT_IMAGES . $index;
 		// phpcs:ignore WordPress.Security.NonceVerification.Missing -- Nonce verification is handled in save_product_variation_edit_fields method
-		$image_ids    = isset( $_POST[ $posted_param ] ) ? sanitize_text_field( wp_unslash( $_POST[ $posted_param ] ) ) : '';
+		$image_ids = isset( $_POST[ $posted_param ] ) ? sanitize_text_field( wp_unslash( $_POST[ $posted_param ] ) ) : '';
+
+		// Validate the image limit for Facebook catalog
+		if ( ! empty( $image_ids ) ) {
+			$image_ids_array = array_filter( array_map( 'trim', explode( ',', $image_ids ) ), 'is_numeric' );
+			if ( count( $image_ids_array ) > self::MAX_FACEBOOK_IMAGES ) {
+				add_action(
+					'admin_notices',
+					function () {
+						$max_images = self::MAX_FACEBOOK_IMAGES;
+						echo '<div class="notice notice-error is-dismissible"><p>' .
+						/* translators: %d: Maximum number of images allowed */
+						sprintf( esc_html__( 'Facebook for WooCommerce: You can only select a maximum of %1$d images for Facebook catalog sync. Only the first %2$d images will be saved.', 'facebook-for-woocommerce' ), esc_html( $max_images ), esc_html( $max_images ) ) .
+						'</p></div>';
+					}
+				);
+				// Limit to maximum allowed images
+				$image_ids_array = array_slice( $image_ids_array, 0, self::MAX_FACEBOOK_IMAGES );
+				$image_ids       = implode( ',', $image_ids_array );
+			}
+		}
 		$posted_param = 'variable_' . \WC_Facebook_Product::FB_PRODUCT_PRICE;
 		// phpcs:ignore WordPress.Security.NonceVerification.Missing -- Nonce verification is handled in save_product_variation_edit_fields method
-		$price        = isset( $_POST[ $posted_param ][ $index ] ) ? wc_format_decimal( wc_clean( wp_unslash( $_POST[ $posted_param ][ $index ] ) ) ) : '';
+		$price = isset( $_POST[ $posted_param ][ $index ] ) ? wc_format_decimal( wc_clean( wp_unslash( $_POST[ $posted_param ][ $index ] ) ) ) : '';
 
 		return array(
 			'description_plain' => $description_plain,
diff --git a/tests/Unit/AdminTest.php b/tests/Unit/AdminTest.php
index 5c63b1b05..687890e7b 100644
--- a/tests/Unit/AdminTest.php
+++ b/tests/Unit/AdminTest.php
@@ -658,4 +658,46 @@ public function test_multiple_images_persistence() {
         $restored_images = get_post_meta($variation_id, \WC_Facebook_Product::FB_PRODUCT_IMAGES, true);
         $this->assertEquals('400,500,600,700', $restored_images);
     }
+
+    /**
+     * Test 21 image limit validation in save_product_variation_edit_fields
+     */
+    public function test_save_product_variation_edit_fields_21_image_limit() {
+        // Create a variable product with variation
+        $variable_product = \WC_Helper_Product::create_variation_product();
+        $variation = wc_get_product($variable_product->get_children()[0]);
+        $variation_id = $variation->get_id();
+        $index = 0;
+
+        // Create a string with 25 image IDs (exceeding the 21 limit)
+        $image_ids_over_limit = implode(',', range(1, 25));
+
+        // Mock POST data with too many images
+        $_POST["facebook_variation_nonce_{$variation_id}"] = wp_create_nonce('facebook_variation_save');
+        $_POST['wc_facebook_sync_mode'] = 'sync_and_show';
+        $_POST['variable_fb_product_image_source'] = [0 => 'multiple'];
+        $_POST["variable_fb_product_images{$index}"] = $image_ids_over_limit;
+
+        // Call the method
+        $this->admin->save_product_variation_edit_fields($variation_id, $index);
+
+        // Verify only first 21 images were saved
+        $saved_images = get_post_meta($variation_id, \WC_Facebook_Product::FB_PRODUCT_IMAGES, true);
+        $saved_ids_array = explode(',', $saved_images);
+        $this->assertEquals(21, count($saved_ids_array));
+        
+        // Verify it's the first 21 images
+        $expected_first_21 = implode(',', range(1, 21));
+        $this->assertEquals($expected_first_21, $saved_images);
+
+        // Test with exactly 21 images (should pass)
+        $exactly_21_images = implode(',', range(100, 120));
+        $_POST["variable_fb_product_images{$index}"] = $exactly_21_images;
+        
+        $this->admin->save_product_variation_edit_fields($variation_id, $index);
+        
+        $saved_images_21 = get_post_meta($variation_id, \WC_Facebook_Product::FB_PRODUCT_IMAGES, true);
+        $this->assertEquals($exactly_21_images, $saved_images_21);
+        $this->assertEquals(21, count(explode(',', $saved_images_21)));
+    }
 }
diff --git a/tests/js/multiple-images.test.js b/tests/js/multiple-images.test.js
index 66e9b44e4..4c443382e 100644
--- a/tests/js/multiple-images.test.js
+++ b/tests/js/multiple-images.test.js
@@ -504,4 +504,195 @@ describe('Multiple Images Functionality', function() {
             expect(global.wp).toBeUndefined();
         });
     });
+
+    describe('21 Image Limit Validation', function() {
+        beforeEach(function() {
+            // Setup DOM
+            document.body.innerHTML = `
+                <div id="fb_product_images_selected_thumbnails_0" class="fb-product-images-thumbnails"></div>
+                <input type="hidden" id="variable_fb_product_images0" value="" />
+            `;
+
+            // Mock window.facebook_for_woocommerce_products_admin
+            global.window.facebook_for_woocommerce_products_admin = {
+                max_facebook_images: 21
+            };
+
+            // Mock alert
+            global.alert = jest.fn();
+        });
+
+        it('should enforce 21 image limit in handleVariationImageSelection', function() {
+            // Create mock selection with 25 images (exceeding limit)
+            const mockSelection = {
+                map: jest.fn((callback) => Array.from({length: 25}, (_, i) => callback({ id: i + 1 })))
+            };
+
+            // Mock the handleVariationImageSelection function from the main script
+            const handleVariationImageSelection = function(selection, variationIndex) {
+                const selectedAttachmentIds = selection.map(attachment => attachment.id);
+                
+                // Check if the selection exceeds the Facebook image limit
+                const maxImages = window.facebook_for_woocommerce_products_admin && window.facebook_for_woocommerce_products_admin.max_facebook_images ? 
+                    parseInt(window.facebook_for_woocommerce_products_admin.max_facebook_images) : 21;
+                if (selectedAttachmentIds.length > maxImages) {
+                    alert(`You can only select a maximum of ${maxImages} images for Facebook catalog sync. Please reduce your selection.`);
+                    return;
+                }
+                
+                // Continue with normal processing...
+                const $hiddenField = $(`#variable_fb_product_images${variationIndex}`);
+                if ($hiddenField.length) {
+                    $hiddenField.val(selectedAttachmentIds.join(','));
+                }
+            };
+
+            // Call the function
+            handleVariationImageSelection(mockSelection, 0);
+
+            // Verify alert was called with correct message
+            expect(global.alert).toHaveBeenCalledWith(
+                'You can only select a maximum of 21 images for Facebook catalog sync. Please reduce your selection.'
+            );
+
+            // Verify hidden field was not updated (function returned early)
+            const hiddenField = document.getElementById('variable_fb_product_images0');
+            expect(hiddenField.value).toBe('');
+        });
+
+        it('should allow exactly 21 images', function() {
+            // Create mock selection with exactly 21 images
+            const mockSelection = {
+                map: jest.fn((callback) => Array.from({length: 21}, (_, i) => callback({ id: i + 1 })))
+            };
+
+            // Mock jQuery for this test
+            global.$ = jest.fn((selector) => {
+                if (selector === '#variable_fb_product_images0') {
+                    return {
+                        length: 1,
+                        val: jest.fn((value) => {
+                            if (value !== undefined) {
+                                document.getElementById('variable_fb_product_images0').value = value;
+                            }
+                            return document.getElementById('variable_fb_product_images0').value;
+                        })
+                    };
+                }
+                return { length: 0 };
+            });
+
+            // Mock the handleVariationImageSelection function
+            const handleVariationImageSelection = function(selection, variationIndex) {
+                const selectedAttachmentIds = selection.map(attachment => attachment.id);
+                
+                const maxImages = window.facebook_for_woocommerce_products_admin && window.facebook_for_woocommerce_products_admin.max_facebook_images ? 
+                    parseInt(window.facebook_for_woocommerce_products_admin.max_facebook_images) : 21;
+                if (selectedAttachmentIds.length > maxImages) {
+                    alert(`You can only select a maximum of ${maxImages} images for Facebook catalog sync. Please reduce your selection.`);
+                    return;
+                }
+                
+                const $hiddenField = $(`#variable_fb_product_images${variationIndex}`);
+                if ($hiddenField.length) {
+                    $hiddenField.val(selectedAttachmentIds.join(','));
+                }
+            };
+
+            // Call the function
+            handleVariationImageSelection(mockSelection, 0);
+
+            // Verify alert was not called
+            expect(global.alert).not.toHaveBeenCalled();
+
+            // Verify hidden field was updated correctly
+            const hiddenField = document.getElementById('variable_fb_product_images0');
+            expect(hiddenField.value).toBe('1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21');
+        });
+
+        it('should fall back to default limit when config is not available', function() {
+            // Remove the config
+            global.window.facebook_for_woocommerce_products_admin = undefined;
+
+            // Create mock selection with 25 images
+            const mockSelection = {
+                map: jest.fn((callback) => Array.from({length: 25}, (_, i) => callback({ id: i + 1 })))
+            };
+
+            // Mock the handleVariationImageSelection function
+            const handleVariationImageSelection = function(selection, variationIndex) {
+                const selectedAttachmentIds = selection.map(attachment => attachment.id);
+                
+                const maxImages = window.facebook_for_woocommerce_products_admin && window.facebook_for_woocommerce_products_admin.max_facebook_images ? 
+                    parseInt(window.facebook_for_woocommerce_products_admin.max_facebook_images) : 21;
+                if (selectedAttachmentIds.length > maxImages) {
+                    alert(`You can only select a maximum of ${maxImages} images for Facebook catalog sync. Please reduce your selection.`);
+                    return;
+                }
+            };
+
+            // Call the function
+            handleVariationImageSelection(mockSelection, 0);
+
+            // Verify alert was called with default limit
+            expect(global.alert).toHaveBeenCalledWith(
+                'You can only select a maximum of 21 images for Facebook catalog sync. Please reduce your selection.'
+            );
+        });
+
+        it('should prevent real-time selection beyond 21 images with throttling', function(done) {
+            // Test the real-time validation logic with improved behavior
+            const maxImages = 21;
+            let selectionLength = 21; // Already at limit
+            let isValidating = false;
+            let lastAlertTime = 0;
+            
+            // Mock selection methods
+            const mockModel = { id: 22 };
+            const mockRemove = jest.fn();
+            
+            // Simulate the improved validation logic
+            const validateSelection = function() {
+                if (isValidating) return;
+                
+                if (selectionLength > maxImages) {
+                    isValidating = true;
+                    mockRemove(mockModel);
+                    selectionLength--; // Simulate removal
+                    
+                    const now = Date.now();
+                    if (now - lastAlertTime > 2000) {
+                        lastAlertTime = now;
+                        setTimeout(function() {
+                            alert(`You can only select a maximum of ${maxImages} images for Facebook catalog sync.`);
+                        }, 10);
+                    }
+                    
+                    setTimeout(function() {
+                        isValidating = false;
+                    }, 100);
+                }
+            };
+            
+            // Test adding one more image (22nd)
+            selectionLength++; // Simulate adding
+            validateSelection();
+
+            // Wait for setTimeout to execute
+            setTimeout(function() {
+                // Verify alert was called
+                expect(global.alert).toHaveBeenCalledWith(
+                    'You can only select a maximum of 21 images for Facebook catalog sync.'
+                );
+
+                // Verify remove was called
+                expect(mockRemove).toHaveBeenCalledWith(mockModel);
+
+                // Verify selection stayed at limit
+                expect(selectionLength).toBe(21);
+                
+                done();
+            }, 50);
+        });
+    });
 });
\ No newline at end of file