diff --git a/src/axolotl/utils/mistral/mistral3_processor.py b/src/axolotl/utils/mistral/mistral3_processor.py
index 01e8f9f10..03a155e53 100644
--- a/src/axolotl/utils/mistral/mistral3_processor.py
+++ b/src/axolotl/utils/mistral/mistral3_processor.py
@@ -30,18 +30,8 @@ class Mistral3Processor(ProcessorMixin):
     Wraps HFMistralTokenizer and adds image processing capabilities.
     """
 
-    # TODO(nano): This should be removed in transformers V5
-    attributes = ["tokenizer"]
-    tokenizer_class = "HFMistralTokenizer"
-
     def __init__(self, tokenizer: HFMistralTokenizer):
-        # Don't call super().__init__ to avoid the class validation issue
-        self.tokenizer = tokenizer
-
-    @property
-    def chat_template(self) -> None:
-        """Chat template is not supported. Dummy method to satisfy HuggingFace API."""
-        return None
+        super().__init__(tokenizer)
 
     @property
     def audio_tokenizer(self) -> None:
diff --git a/tests/utils/test_mistral3_processor.py b/tests/utils/test_mistral3_processor.py
new file mode 100644
index 000000000..ae2bc1faf
--- /dev/null
+++ b/tests/utils/test_mistral3_processor.py
@@ -0,0 +1,149 @@
+"""Tests for Mistral3Processor with transformers v5 ProcessorMixin integration"""
+
+from unittest.mock import MagicMock
+
+import pytest
+import torch
+from transformers.feature_extraction_utils import BatchFeature
+
+from axolotl.utils.mistral.mistral3_processor import Mistral3Processor
+from axolotl.utils.mistral.mistral_tokenizer import HFMistralTokenizer
+
+
+@pytest.fixture()
+def mock_tokenizer():
+    """Create a mock HFMistralTokenizer that passes v5 ProcessorMixin isinstance checks."""
+    return MagicMock(spec=HFMistralTokenizer)
+
+
+@pytest.fixture()
+def processor(mock_tokenizer):
+    return Mistral3Processor(tokenizer=mock_tokenizer)
+
+
+class TestMistral3ProcessorInit:
+    def test_tokenizer_is_set(self, processor, mock_tokenizer):
+        assert processor.tokenizer is mock_tokenizer
+
+    def test_chat_template_is_none(self, processor):
+        assert processor.chat_template is None
+
+    def test_audio_tokenizer_is_none(self, processor):
+        assert processor.audio_tokenizer is None
+
+
+class TestApplyChatTemplateTokenized:
+    """Test apply_chat_template with tokenize=True, return_dict=True"""
+
+    @pytest.fixture()
+    def batched_conversations(self):
+        return [
+            [
+                {"role": "user", "content": "Describe this image."},
+                {"role": "assistant", "content": "It is red."},
+            ],
+            [
+                {"role": "user", "content": "What is this?"},
+                {"role": "assistant", "content": "A cat."},
+            ],
+        ]
+
+    def test_returns_batch_feature_with_pixel_values(
+        self, processor, mock_tokenizer, batched_conversations
+    ):
+        pixel_values = torch.randn(2, 3, 224, 224, dtype=torch.float64)
+        mock_tokenizer.apply_chat_template.return_value = {
+            "input_ids": torch.tensor([[1, 2, 3], [4, 5, 6]]),
+            "attention_mask": torch.tensor([[1, 1, 1], [1, 1, 1]]),
+            "pixel_values": pixel_values,
+        }
+
+        result = processor.apply_chat_template(
+            batched_conversations, tokenize=True, return_dict=True
+        )
+
+        assert isinstance(result, BatchFeature)
+        assert "pixel_values" in result
+        assert "image_sizes" in result
+        assert result["pixel_values"].dtype == torch.float32
+        assert result["image_sizes"].shape == (2, 2)
+        assert result["image_sizes"][0].tolist() == [224, 224]
+
+    def test_returns_batch_feature_without_pixel_values(
+        self, processor, mock_tokenizer, batched_conversations
+    ):
+        mock_tokenizer.apply_chat_template.return_value = {
+            "input_ids": torch.tensor([[1, 2, 3], [4, 5, 6]]),
+            "attention_mask": torch.tensor([[1, 1, 1], [1, 1, 1]]),
+        }
+
+        result = processor.apply_chat_template(
+            batched_conversations, tokenize=True, return_dict=True
+        )
+
+        assert isinstance(result, BatchFeature)
+        assert "input_ids" in result
+        assert "image_sizes" not in result
+
+
+class TestApplyChatTemplateNotTokenized:
+    def test_single_conversation_returns_unwrapped(self, processor, mock_tokenizer):
+        """Single conversation (not batched) should return unwrapped result."""
+        single_conversation = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": "Hi"},
+        ]
+        mock_tokenizer.apply_chat_template.return_value = [
+            "<s>[INST]Hello[/INST]Hi</s>"
+        ]
+
+        result = processor.apply_chat_template(
+            single_conversation, tokenize=False, return_dict=False
+        )
+
+        assert result == "<s>[INST]Hello[/INST]Hi</s>"
+
+    def test_batched_conversations_returns_list(self, processor, mock_tokenizer):
+        batched = [
+            [
+                {"role": "user", "content": "Hello"},
+                {"role": "assistant", "content": "Hi"},
+            ],
+            [
+                {"role": "user", "content": "Bye"},
+                {"role": "assistant", "content": "Bye"},
+            ],
+        ]
+        mock_tokenizer.apply_chat_template.return_value = ["text1", "text2"]
+
+        result = processor.apply_chat_template(
+            batched, tokenize=False, return_dict=False
+        )
+
+        assert result == ["text1", "text2"]
+
+
+class TestCall:
+    def test_delegates_to_tokenizer(self, processor, mock_tokenizer):
+        mock_tokenizer.return_value = {
+            "input_ids": [1, 2, 3],
+            "attention_mask": [1, 1, 1],
+        }
+
+        result = processor("Hello world")
+
+        mock_tokenizer.assert_called_once()
+        assert isinstance(result, BatchFeature)
+
+
+class TestReturnTensorsValidation:
+    def test_rejects_non_pt_return_tensors(self, processor):
+        conversation = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": "Hi"},
+        ]
+
+        with pytest.raises(ValueError, match=r"only supports.*return_tensors='pt'"):
+            processor.apply_chat_template(
+                conversation, tokenize=True, return_dict=True, return_tensors="np"
+            )