diff --git a/python/sglang/srt/configs/model_config.py b/python/sglang/srt/configs/model_config.py
index 111145ef6d2f..5601c18da60d 100644
--- a/python/sglang/srt/configs/model_config.py
+++ b/python/sglang/srt/configs/model_config.py
@@ -219,6 +219,8 @@ def __init__(
             mm_disabled_models = [
                 "Gemma3ForConditionalGeneration",
                 "Llama4ForConditionalGeneration",
+                "Qwen3_5ForConditionalGeneration",
+                "Qwen3_5MoeForConditionalGeneration",
                 "Step3VLForConditionalGeneration",
             ]
             if (
diff --git a/test/registered/unit/configs/test_qwen3_5_model_config.py b/test/registered/unit/configs/test_qwen3_5_model_config.py
new file mode 100644
index 000000000000..0ab66004539d
--- /dev/null
+++ b/test/registered/unit/configs/test_qwen3_5_model_config.py
@@ -0,0 +1,75 @@
+"""Unit tests for Qwen3.5 ModelConfig defaults."""
+
+import json
+import tempfile
+from pathlib import Path
+
+from sglang.srt.configs.model_config import ModelConfig
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=1, suite="base-a-test-cpu")
+
+
+def _write_qwen3_5_config(model_dir: Path, architecture: str):
+    config = {
+        "architectures": [architecture],
+        "model_type": "qwen3_5_moe"
+        if architecture == "Qwen3_5MoeForConditionalGeneration"
+        else "qwen3_5",
+        "text_config": {
+            "model_type": "qwen3_5_moe_text"
+            if architecture == "Qwen3_5MoeForConditionalGeneration"
+            else "qwen3_5_text",
+            "hidden_size": 64,
+            "intermediate_size": 128,
+            "max_position_embeddings": 1024,
+            "num_attention_heads": 4,
+            "num_hidden_layers": 2,
+            "num_key_value_heads": 1,
+            "rope_parameters": {"rope_type": "default"},
+            "vocab_size": 128,
+        },
+        "vision_config": {"model_type": "qwen3_5"},
+    }
+    (model_dir / "config.json").write_text(json.dumps(config))
+    (model_dir / "generation_config.json").write_text(
+        json.dumps({"eos_token_id": 1, "pad_token_id": 0})
+    )
+
+
+class TestQwen3_5ModelConfig(CustomTestCase):
+    def test_qwen3_5_text_architectures_disable_multimodal_by_default(self):
+        for architecture in [
+            "Qwen3_5ForConditionalGeneration",
+            "Qwen3_5MoeForConditionalGeneration",
+        ]:
+            with self.subTest(architecture=architecture):
+                with tempfile.TemporaryDirectory() as tmpdir:
+                    model_dir = Path(tmpdir)
+                    _write_qwen3_5_config(model_dir, architecture)
+
+                    model_config = ModelConfig(str(model_dir), trust_remote_code=True)
+
+                    self.assertFalse(model_config.is_multimodal)
+                    self.assertFalse(model_config.is_image_understandable_model)
+
+    def test_qwen3_5_can_still_opt_in_to_multimodal(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            model_dir = Path(tmpdir)
+            _write_qwen3_5_config(
+                model_dir, "Qwen3_5MoeForConditionalGeneration"
+            )
+
+            model_config = ModelConfig(
+                str(model_dir), trust_remote_code=True, enable_multimodal=True
+            )
+
+            self.assertTrue(model_config.is_multimodal)
+            self.assertTrue(model_config.is_image_understandable_model)
+
+
+if __name__ == "__main__":
+    import unittest
+
+    unittest.main()