diff --git a/flexeval/core/eval_setups.py b/flexeval/core/eval_setups.py
index e922b5e7..b4822629 100644
--- a/flexeval/core/eval_setups.py
+++ b/flexeval/core/eval_setups.py
@@ -50,6 +50,7 @@ class ChatResponse(EvalSetup):
     metrics: list[Metric] | Metric | None = None
     batch_size: int = 4
     max_instances: int | None = None
+    random_seed: int = 42
 
     def evaluate_lm(
         self,
@@ -60,6 +61,8 @@ def evaluate_lm(
             metrics = [metrics]
         metrics += [FinishReasonCount(), OutputLengthStats()]
 
+        language_model.set_random_seed(self.random_seed)
+
         return evaluate_chat_response(
             language_model=language_model,
             gen_kwargs=self.gen_kwargs,
@@ -85,6 +88,7 @@ class Generation(EvalSetup):
     metrics: list[Metric] | Metric | None = None
     batch_size: int = 4
     max_instances: int | None = None
+    random_seed: int = 42
 
     def __post_init__(self) -> None:
         if isinstance(self.prompt_template, str):
@@ -99,6 +103,8 @@ def evaluate_lm(
             metrics = [metrics]
         metrics += [FinishReasonCount(), OutputLengthStats()]
 
+        language_model.set_random_seed(self.random_seed)
+
         return evaluate_generation(
             language_model=language_model,
             gen_kwargs=self.gen_kwargs,
diff --git a/flexeval/core/language_model/base.py b/flexeval/core/language_model/base.py
index 58fa6a20..0993b418 100644
--- a/flexeval/core/language_model/base.py
+++ b/flexeval/core/language_model/base.py
@@ -66,6 +66,13 @@ def __init__(
         self.string_processors = string_processors
         self.tools = tools
 
+    def set_random_seed(self, seed: int) -> None:
+        """
+        A method to set random seed for deterministic behavior.
+        """
+        msg = "set_random_seed is not implemented."
+        raise NotImplementedError(msg)
+
     def _batch_complete_text(
         self,
         text_list: list[str],
diff --git a/flexeval/core/language_model/hf_lm.py b/flexeval/core/language_model/hf_lm.py
index f1a31c48..ae8e09fb 100644
--- a/flexeval/core/language_model/hf_lm.py
+++ b/flexeval/core/language_model/hf_lm.py
@@ -229,6 +229,9 @@ def __init__(
         logger.info(f"random seed: {random_seed}")
         transformers.set_seed(random_seed)
 
+    def set_random_seed(self, seed: int) -> None:
+        transformers.set_seed(seed)
+
     @staticmethod
     def load_model(method: Callable) -> Callable:
         """Decorator to load the model lazily."""
diff --git a/flexeval/core/language_model/litellm_api.py b/flexeval/core/language_model/litellm_api.py
index 887619ed..15301e63 100644
--- a/flexeval/core/language_model/litellm_api.py
+++ b/flexeval/core/language_model/litellm_api.py
@@ -68,6 +68,9 @@ def __init__(
         )
         self.ignore_seed = ignore_seed
 
+    def set_random_seed(self, seed: int) -> None:
+        self.default_gen_kwargs["seed"] = seed
+
     def _batch_complete_text(
         self,
         text_list: list[str],
diff --git a/flexeval/core/language_model/openai_api.py b/flexeval/core/language_model/openai_api.py
index 477a55d7..e957bf56 100644
--- a/flexeval/core/language_model/openai_api.py
+++ b/flexeval/core/language_model/openai_api.py
@@ -119,6 +119,9 @@ def __init__(
         self.first_wait_time = first_wait_time
         self.max_wait_time = max_wait_time
 
+    def set_random_seed(self, seed: int) -> None:
+        self.default_gen_kwargs["seed"] = seed
+
     def _parallel_run_chatgpt(
         self,
         messages_list: list[list[dict[str, Any]]],
@@ -414,6 +417,9 @@ def _parallel_run_chatgpt(
             ]
         return [future.result() for future in futures]
 
+    def set_random_seed(self, seed: int) -> None:
+        self.default_gen_kwargs["seed"] = seed
+
     def _batch_complete_text(
         self,
         text_list: list[str],
diff --git a/flexeval/core/language_model/vllm_model.py b/flexeval/core/language_model/vllm_model.py
index a16d307a..aa9cb245 100644
--- a/flexeval/core/language_model/vllm_model.py
+++ b/flexeval/core/language_model/vllm_model.py
@@ -156,6 +156,9 @@ def wrapper(self: VLLM, *args: tuple, **kwargs: dict) -> Callable:
 
         return wrapper
 
+    def set_random_seed(self, seed: int) -> None:
+        self.default_gen_kwargs["seed"] = seed
+
     @load_model
     def _batch_complete_text(
         self,
diff --git a/tests/core/language_model/test_hf_lm.py b/tests/core/language_model/test_hf_lm.py
index 388041fd..591285fc 100644
--- a/tests/core/language_model/test_hf_lm.py
+++ b/tests/core/language_model/test_hf_lm.py
@@ -232,6 +232,24 @@ def test_if_random_seed_fixes_the_lm_outputs(lm_init_func: Callable[..., Hugging
     assert len(completions) > 1
 
 
+def test_if_set_random_seed_fixes_the_lm_outputs(lm: HuggingFaceLM) -> None:
+    # first check if the outputs are different without fixing the seed
+    completions = set()
+    for i in range(3):
+        lm.set_random_seed(i)
+        completion = lm.complete_text(["<s>"], do_sample=True)[0]
+        completions.add(completion.text)
+    assert len(completions) > 1
+
+    # then check if the outputs are the same with fixing the seed
+    completions = set()
+    for _ in range(3):
+        lm.set_random_seed(42)
+        completion = lm.complete_text(["<s>"], do_sample=True)[0]
+        completions.add(completion.text)
+    assert len(completions) == 1
+
+
 def test_if_custom_chat_template_is_given(lm_init_func: Callable[..., HuggingFaceLM]) -> None:
     # To verify that the template specified in `custom_chat_template` is passed to `tokenizer.apply_chat_template()`,
     # prepare a template where the model is expected to output "0 0..." for any input.
@@ -494,3 +512,8 @@ def mock_apply_chat_template(messages: list[list[dict[str, Any]]], **kwargs) ->
     finally:
         # Restore original method
         chat_lm_with_system_message.tokenizer.apply_chat_template = original_apply_chat_template
+
+
+def test_set_random_seed(lm: HuggingFaceLM) -> None:
+    # check that method is implemented
+    assert lm.set_random_seed(42) is None
diff --git a/tests/core/language_model/test_litellm_api.py b/tests/core/language_model/test_litellm_api.py
index 06894d5c..49dde7dc 100644
--- a/tests/core/language_model/test_litellm_api.py
+++ b/tests/core/language_model/test_litellm_api.py
@@ -86,3 +86,9 @@ def test_if_not_ignore_seed() -> None:
     with patch.object(OpenAIChatAPI, "_batch_complete_text", return_value=[LMOutput("ChatGPT.")]) as mock_method:
         chat_lm.complete_text(text, stop_sequences=None, max_new_tokens=None, temperature=0.7, seed=42)
         mock_method.assert_called_once_with([text], None, None, temperature=0.7, seed=42)
+
+
+@pytest.mark.skipif(not is_openai_enabled(), reason="OpenAI is not installed")
+def test_set_random_seed(chat_lm: OpenAIChatAPI) -> None:
+    chat_lm.set_random_seed(42)
+    assert chat_lm.default_gen_kwargs["seed"] == 42
diff --git a/tests/core/language_model/test_openai_api.py b/tests/core/language_model/test_openai_api.py
index 3f3346da..07e0d7cd 100644
--- a/tests/core/language_model/test_openai_api.py
+++ b/tests/core/language_model/test_openai_api.py
@@ -161,3 +161,9 @@ def test_model_limit_new_tokens_complete_text(chat_lm: OpenAIChatAPI, caplog: py
     assert len(caplog.records) >= 1
     assert any(record.msg.startswith("The specified `max_new_tokens` (128) exceeds") for record in caplog.records)
     caplog.clear()
+
+
+@pytest.mark.skipif(not is_openai_enabled(), reason="OpenAI is not installed")
+def test_set_random_seed(chat_lm: OpenAIChatAPI) -> None:
+    chat_lm.set_random_seed(42)
+    assert chat_lm.default_gen_kwargs["seed"] == 42
diff --git a/tests/core/language_model/vllm/test_vllm_serve_lm.py b/tests/core/language_model/vllm/test_vllm_serve_lm.py
index 72a3700b..b68a3952 100644
--- a/tests/core/language_model/vllm/test_vllm_serve_lm.py
+++ b/tests/core/language_model/vllm/test_vllm_serve_lm.py
@@ -115,3 +115,9 @@ def test_generate_chat_response_if_number_of_tools_and_messages_not_equal(
         self, chat_lm_for_tool_calling: LanguageModel
     ) -> None:
         pass
+
+
+@pytest.mark.skipif(not is_vllm_enabled(), reason="vllm library is not installed")
+def test_set_random_seed(chat_lm: VLLMServeLM) -> None:
+    chat_lm.set_random_seed(42)
+    assert chat_lm.default_gen_kwargs["seed"] == 42
diff --git a/tests/core/language_model/vllm/test_vllm_specific.py b/tests/core/language_model/vllm/test_vllm_specific.py
index b1edca6e..f4ee6a95 100644
--- a/tests/core/language_model/vllm/test_vllm_specific.py
+++ b/tests/core/language_model/vllm/test_vllm_specific.py
@@ -232,3 +232,9 @@ def mock_apply_chat_template(messages: list[list[dict[str, Any]]], **kwargs) ->
     finally:
         # Restore original method
         chat_lm_with_system_message.tokenizer.apply_chat_template = original_apply_chat_template
+
+
+@pytest.mark.skipif(not is_vllm_enabled(), reason="vllm library is not installed")
+def test_set_random_seed(chat_lm: VLLM) -> None:
+    chat_lm.set_random_seed(42)
+    assert chat_lm.default_gen_kwargs["seed"] == 42
diff --git a/tests/dummy_modules/lm.py b/tests/dummy_modules/lm.py
index c189ca0d..2790b6d1 100644
--- a/tests/dummy_modules/lm.py
+++ b/tests/dummy_modules/lm.py
@@ -23,6 +23,9 @@ def _batch_compute_log_probs(
     ) -> list[float]:
         return [-1.0] * len(text_list)
 
+    def set_random_seed(self, seed: int) -> None:
+        pass
+
     def _batch_generate_chat_response(
         self,
         chat_messages_list: list[list[dict[str, str]]],
diff --git a/tests/dummy_modules/reward_lm.py b/tests/dummy_modules/reward_lm.py
index d6257d5a..b1cd76c8 100644
--- a/tests/dummy_modules/reward_lm.py
+++ b/tests/dummy_modules/reward_lm.py
@@ -11,6 +11,9 @@ def __init__(self, response: str = "[[A]]") -> None:
         super().__init__()
         self.response = response
 
+    def set_random_seed(self, seed: int) -> None:
+        pass
+
     def _batch_complete_text(self, text_list: list[str], **kwargs) -> list[LMOutput]:
         return [LMOutput(text=self.response, finish_reason="length") for _ in text_list]