diff --git a/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/main/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutor.java b/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/main/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutor.java
index 909a19f587..27aca98648 100644
--- a/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/main/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutor.java
+++ b/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/main/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutor.java
@@ -128,7 +128,7 @@ private AgentRequestOptions buildAgentRequestOptions(RequestContext context) {
         AgentRequestOptions requestOptions = new AgentRequestOptions();
         requestOptions.setTaskId(context.getTaskId());
         requestOptions.setUserId(getUserId(message));
-        requestOptions.setSessionId(getSessionId(message));
+        requestOptions.setSessionId(getSessionId(context, message));
         return requestOptions;
     }
 
@@ -139,7 +139,29 @@ private String getUserId(Message message) {
         return "";
     }
 
-    private String getSessionId(Message message) {
+    /**
+     * Extract sessionId from the A2A request.
+     *
+     * <p>Resolution order:
+     * <ol>
+     *     <li>A2A protocol standard field: {@code Message.contextId} (via {@code RequestContext.getContextId()}).</li>
+     *     <li>Backward-compatible fallback: {@code Message.metadata["sessionId"]}.</li>
+     * </ol>
+     *
+     * <p>This ensures any standard A2A client that sets {@code contextId} on the message
+     * can be correctly routed to per-session state without requiring a custom metadata key.
+     *
+     * @param context the request context containing the resolved contextId
+     * @param message the original A2A message
+     * @return the sessionId, or empty string if not found
+     */
+    private String getSessionId(RequestContext context, Message message) {
+        // Prefer the protocol-standard contextId field
+        String contextId = context.getContextId();
+        if (contextId != null && !contextId.isEmpty()) {
+            return contextId;
+        }
+        // Backward-compatible fallback: read from metadata
         if (message.getMetadata() != null && message.getMetadata().containsKey("sessionId")) {
             return String.valueOf(message.getMetadata().get("sessionId"));
         }
diff --git a/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/test/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutorTest.java b/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/test/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutorTest.java
index 976d85a7a4..2f4f1fbcf7 100644
--- a/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/test/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutorTest.java
+++ b/agentscope-extensions/agentscope-extensions-protocol/agentscope-extensions-a2a/agentscope-extensions-a2a-server/src/test/java/io/agentscope/core/a2a/server/executor/AgentScopeAgentExecutorTest.java
@@ -551,6 +551,150 @@ void testHandleExceptionDuringTaskCancellation() throws JSONRPCError {
         }
     }
 
+    @Nested
+    @DisplayName("Session ID Resolution Tests")
+    class SessionIdResolutionTests {
+
+        @Test
+        @DisplayName("Should use contextId as sessionId when contextId is present")
+        void testSessionIdFromContextId() throws JSONRPCError {
+            // Given: contextId is set, no metadata sessionId
+            String taskId = UUID.randomUUID().toString();
+            String contextId = "context-session-123";
+
+            when(mockContext.getTaskId()).thenReturn(taskId);
+            when(mockContext.getContextId()).thenReturn(contextId);
+
+            Message mockMessage = mock(Message.class);
+            when(mockMessage.getTaskId()).thenReturn(taskId);
+            when(mockMessage.getContextId()).thenReturn(contextId);
+            when(mockMessage.getParts()).thenReturn(List.of(new TextPart("hello")));
+            when(mockMessage.getMetadata()).thenReturn(null); // No metadata at all
+            when(mockContext.getMessage()).thenReturn(mockMessage);
+
+            MessageSendParams mockParams = mock(MessageSendParams.class);
+            when(mockContext.getParams()).thenReturn(mockParams);
+            when(mockParams.message()).thenReturn(mockMessage);
+
+            when(mockContext.getCallContext()).thenReturn(serverCallContext);
+            when(serverCallContext.getState()).thenReturn(Map.of());
+
+            AtomicReference<AgentRequestOptions> capturedOptions = new AtomicReference<>();
+            when(mockAgentRunner.stream(anyList(), any(AgentRequestOptions.class)))
+                    .thenAnswer(
+                            invocation -> {
+                                capturedOptions.set(invocation.getArgument(1));
+                                return Flux.just(
+                                        new Event(
+                                                EventType.REASONING,
+                                                Msg.builder().textContent("response").build(),
+                                                true));
+                            });
+
+            doAnswer(invocation -> null).when(mockEventQueue).enqueueEvent(any(Message.class));
+
+            // When
+            executor.execute(mockContext, mockEventQueue);
+
+            // Then: sessionId should come from contextId
+            assertNotNull(capturedOptions.get());
+            assertEquals(contextId, capturedOptions.get().getSessionId());
+        }
+
+        @Test
+        @DisplayName("Should fallback to metadata sessionId when contextId is empty")
+        void testSessionIdFallbackToMetadata() throws JSONRPCError {
+            // Given: contextId is empty, metadata has sessionId
+            String taskId = UUID.randomUUID().toString();
+            String metadataSessionId = "metadata-session-456";
+
+            when(mockContext.getTaskId()).thenReturn(taskId);
+            when(mockContext.getContextId()).thenReturn(""); // Empty contextId
+
+            Message mockMessage = mock(Message.class);
+            when(mockMessage.getTaskId()).thenReturn(taskId);
+            when(mockMessage.getContextId()).thenReturn("");
+            when(mockMessage.getParts()).thenReturn(List.of(new TextPart("hello")));
+            when(mockMessage.getMetadata()).thenReturn(Map.of("sessionId", metadataSessionId));
+            when(mockContext.getMessage()).thenReturn(mockMessage);
+
+            MessageSendParams mockParams = mock(MessageSendParams.class);
+            when(mockContext.getParams()).thenReturn(mockParams);
+            when(mockParams.message()).thenReturn(mockMessage);
+
+            when(mockContext.getCallContext()).thenReturn(serverCallContext);
+            when(serverCallContext.getState()).thenReturn(Map.of());
+
+            AtomicReference<AgentRequestOptions> capturedOptions = new AtomicReference<>();
+            when(mockAgentRunner.stream(anyList(), any(AgentRequestOptions.class)))
+                    .thenAnswer(
+                            invocation -> {
+                                capturedOptions.set(invocation.getArgument(1));
+                                return Flux.just(
+                                        new Event(
+                                                EventType.REASONING,
+                                                Msg.builder().textContent("response").build(),
+                                                true));
+                            });
+
+            doAnswer(invocation -> null).when(mockEventQueue).enqueueEvent(any(Message.class));
+
+            // When
+            executor.execute(mockContext, mockEventQueue);
+
+            // Then: sessionId should fallback to metadata
+            assertNotNull(capturedOptions.get());
+            assertEquals(metadataSessionId, capturedOptions.get().getSessionId());
+        }
+
+        @Test
+        @DisplayName("Should prefer contextId over metadata sessionId when both present")
+        void testContextIdTakesPrecedenceOverMetadata() throws JSONRPCError {
+            // Given: both contextId and metadata sessionId are set
+            String taskId = UUID.randomUUID().toString();
+            String contextId = "context-id-wins";
+            String metadataSessionId = "metadata-id-loses";
+
+            when(mockContext.getTaskId()).thenReturn(taskId);
+            when(mockContext.getContextId()).thenReturn(contextId);
+
+            Message mockMessage = mock(Message.class);
+            when(mockMessage.getTaskId()).thenReturn(taskId);
+            when(mockMessage.getContextId()).thenReturn(contextId);
+            when(mockMessage.getParts()).thenReturn(List.of(new TextPart("hello")));
+            when(mockMessage.getMetadata()).thenReturn(Map.of("sessionId", metadataSessionId));
+            when(mockContext.getMessage()).thenReturn(mockMessage);
+
+            MessageSendParams mockParams = mock(MessageSendParams.class);
+            when(mockContext.getParams()).thenReturn(mockParams);
+            when(mockParams.message()).thenReturn(mockMessage);
+
+            when(mockContext.getCallContext()).thenReturn(serverCallContext);
+            when(serverCallContext.getState()).thenReturn(Map.of());
+
+            AtomicReference<AgentRequestOptions> capturedOptions = new AtomicReference<>();
+            when(mockAgentRunner.stream(anyList(), any(AgentRequestOptions.class)))
+                    .thenAnswer(
+                            invocation -> {
+                                capturedOptions.set(invocation.getArgument(1));
+                                return Flux.just(
+                                        new Event(
+                                                EventType.REASONING,
+                                                Msg.builder().textContent("response").build(),
+                                                true));
+                            });
+
+            doAnswer(invocation -> null).when(mockEventQueue).enqueueEvent(any(Message.class));
+
+            // When
+            executor.execute(mockContext, mockEventQueue);
+
+            // Then: contextId should take precedence
+            assertNotNull(capturedOptions.get());
+            assertEquals(contextId, capturedOptions.get().getSessionId());
+        }
+    }
+
     @Test
     @DisplayName("Should handle exception during execution")
     void testHandleExceptionDuringExecution() throws JSONRPCError {