diff --git a/superset/mcp_service/sql_lab/schemas.py b/superset/mcp_service/sql_lab/schemas.py
index f328a752fc7..f7c25266fdb 100644
--- a/superset/mcp_service/sql_lab/schemas.py
+++ b/superset/mcp_service/sql_lab/schemas.py
@@ -108,6 +108,27 @@ class ColumnInfo(BaseModel):
     type: str = Field(..., description="Column data type")
     is_nullable: bool | None = Field(None, description="Whether column allows NULL")
 
+    @field_validator("is_nullable", mode="before")
+    @classmethod
+    def coerce_is_nullable(cls, v: Any) -> bool | None:
+        """Coerce non-boolean values (e.g. Athena's 'UNKNOWN') to None."""
+        if v is None or isinstance(v, bool):
+            return v
+        if isinstance(v, (int, float)):
+            if v == 1:
+                return True
+            if v == 0:
+                return False
+            return None
+        if isinstance(v, str):
+            lowered = v.strip().lower()
+            if lowered in ("true", "1", "yes"):
+                return True
+            if lowered in ("false", "0", "no"):
+                return False
+            return None
+        return None
+
 
 class StatementData(BaseModel):
     """Row data and column metadata for a single SQL statement."""
diff --git a/tests/unit_tests/mcp_service/sql_lab/tool/test_execute_sql.py b/tests/unit_tests/mcp_service/sql_lab/tool/test_execute_sql.py
index 697bec39d59..e1d3dee8e39 100644
--- a/tests/unit_tests/mcp_service/sql_lab/tool/test_execute_sql.py
+++ b/tests/unit_tests/mcp_service/sql_lab/tool/test_execute_sql.py
@@ -34,6 +34,7 @@ from fastmcp.exceptions import ToolError
 from superset_core.queries.types import QueryResult, QueryStatus, StatementResult
 
 from superset.mcp_service.app import mcp
+from superset.mcp_service.sql_lab.schemas import ColumnInfo
 
 logging.basicConfig(level=logging.DEBUG)
 logger = logging.getLogger(__name__)
@@ -1164,3 +1165,56 @@ class TestExecuteSqlOAuth2:
             assert data["success"] is False
             assert "configuration" in data["error"]
             assert data["error_type"] == "OAUTH2_REDIRECT_ERROR"
+
+
+class TestColumnInfoIsNullable:
+    """Tests for ColumnInfo.is_nullable coercion (Athena returns 'UNKNOWN')."""
+
+    def test_unknown_string_becomes_none(self):
+        assert (
+            ColumnInfo(name="c", type="int", is_nullable="UNKNOWN").is_nullable is None
+        )
+
+    def test_arbitrary_string_becomes_none(self):
+        assert ColumnInfo(name="c", type="int", is_nullable="maybe").is_nullable is None
+
+    def test_true_bool(self):
+        assert ColumnInfo(name="c", type="int", is_nullable=True).is_nullable is True
+
+    def test_false_bool(self):
+        assert ColumnInfo(name="c", type="int", is_nullable=False).is_nullable is False
+
+    def test_none(self):
+        assert ColumnInfo(name="c", type="int", is_nullable=None).is_nullable is None
+
+    def test_default_is_none(self):
+        assert ColumnInfo(name="c", type="int").is_nullable is None
+
+    def test_true_string(self):
+        assert ColumnInfo(name="c", type="int", is_nullable="true").is_nullable is True
+
+    def test_false_string(self):
+        assert (
+            ColumnInfo(name="c", type="int", is_nullable="false").is_nullable is False
+        )
+
+    def test_one_string(self):
+        assert ColumnInfo(name="c", type="int", is_nullable="1").is_nullable is True
+
+    def test_zero_string(self):
+        assert ColumnInfo(name="c", type="int", is_nullable="0").is_nullable is False
+
+    def test_integer_one(self):
+        assert ColumnInfo(name="c", type="int", is_nullable=1).is_nullable is True
+
+    def test_integer_zero(self):
+        assert ColumnInfo(name="c", type="int", is_nullable=0).is_nullable is False
+
+    def test_integer_two_becomes_none(self):
+        assert ColumnInfo(name="c", type="int", is_nullable=2).is_nullable is None
+
+    def test_model_validate_unknown(self):
+        col = ColumnInfo.model_validate(
+            {"name": "c", "type": "int", "is_nullable": "UNKNOWN"}
+        )
+        assert col.is_nullable is None