diff --git a/docs/source/grpo_trainer.md b/docs/source/grpo_trainer.md
index 973dadf03a..af54406dfe 100644
--- a/docs/source/grpo_trainer.md
+++ b/docs/source/grpo_trainer.md
@@ -149,28 +149,33 @@ You can test it as follows:
 
 #### Example 2: Conversational format
 
-For conversational format, completions consist of structured messages. Here’s an example that rewards longer completion content:
+For conversational format, completions consist of structured messages. Here’s an example of reward function that checks if the completion has a specific format. This example is inspired by the reward function used in the paper [DeepSeek-R1: Incentivizing Reasoning Capability in LLMs via Reinforcement Learning](https://huggingface.co/papers/2501.12948).
 
 ```python
-def reward_func(prompts, completions):
-    """Reward function that gives higher scores to longer completion content."""
+import re
+
+def format_reward_func(prompts, completions):
+    """Reward function that checks if the completion has a specific format."""
+    pattern = r"^<think>.*?</think><answer>.*?</answer>$"
     completion_contents = [completion[0]["content"] for completion in completions]
-    return [float(len(content)) for content in completion_contents]
+    matches = [re.match(pattern, content) for content in completion_contents]
+    return [1.0 if match else 0.0 for match in matches]
 ```
 
 You can test this function as follows:
 
 ```python
 >>> prompts = [
-...     [{"role": "user", "content": "What color is the sky?"}],
-...     [{"role": "user", "content": "Where is the sun?"}],
+...     [{"role": "assistant", "content": "What is the result of (1 + 2) * 4?"}],
+...     [{"role": "assistant", "content": "What is the result of (3 + 1) * 2?"}],
 ... ]
 >>> completions = [
-...     [{"role": "assistant", "content": "It is blue."}],
-...     [{"role": "assistant", "content": "In the sky."}],
+...     [{"role": "assistant", "content": "<think>The sum of 1 and 2 is 3, which we multiply by 4 to get 12.</think><answer>(1 + 2) * 4 = 12</answer>"}],
+...     [{"role": "assistant", "content": "The sum of 3 and 1 is 4, which we multiply by 2 to get 8. So (3 + 1) * 2 = 8."}],
 ... ]
->>> print(reward_func(prompts, completions))
-[11.0, 11.0]
+>>> format_reward_func(prompts, completions)
+[1.0, 0.0]
+>>>
 ```
 
 #### Passing the reward function to the trainer