diff --git a/sdk/evaluation/azure-ai-evaluation/CHANGELOG.md b/sdk/evaluation/azure-ai-evaluation/CHANGELOG.md
index 22f49dc3c2b3..0d87e5da3c59 100644
--- a/sdk/evaluation/azure-ai-evaluation/CHANGELOG.md
+++ b/sdk/evaluation/azure-ai-evaluation/CHANGELOG.md
@@ -14,6 +14,7 @@
 
 ### Bugs Fixed
 
+- Fixed error blame attribution in `_get_single_run_results` to perform a case-insensitive comparison when checking the AOAI error code for `UserError`, ensuring failed evaluation runs are correctly classified as user errors regardless of server-side casing.
 - Fixed `evaluate()` raising `EvaluationException: (InternalError) unhashable type: 'list'` when an evaluator emitted a list value under a `_result`-suffixed column. Binary aggregation now skips such columns with a warning instead of aborting the entire run.
 - Fixed row classification double-counting in `_calculate_aoai_evaluation_summary` where errored rows were counted separately and could also be counted as passed/failed. Rows are now classified into mutually exclusive buckets with priority: passed > failed > errored > skipped.
 - Fixed row classification where rows with empty or missing results lists were incorrectly counted as "passed" (the condition `passed_count == len(results) - error_count` evaluated `0 == 0` as True).
diff --git a/sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_evaluate/_evaluate_aoai.py b/sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_evaluate/_evaluate_aoai.py
index b0d3fb405746..6d44320f9f9a 100644
--- a/sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_evaluate/_evaluate_aoai.py
+++ b/sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_evaluate/_evaluate_aoai.py
@@ -307,10 +307,16 @@ def _get_single_run_results(
 
     LOGGER.info(f"AOAI: Eval run {run_info['eval_run_id']} completed with status: {run_results.status}")
     if run_results.status != "completed":
+        error_code = getattr(getattr(run_results, "error", None), "code", None)
+        blame = (
+            ErrorBlame.USER_ERROR
+            if isinstance(error_code, str) and error_code.lower() == "usererror"
+            else ErrorBlame.UNKNOWN
+        )
         raise EvaluationException(
             message=f"AOAI evaluation run {run_info['eval_group_id']}/{run_info['eval_run_id']}"
             + f" failed with status {run_results.status}.",
-            blame=ErrorBlame.UNKNOWN,
+            blame=blame,
             category=ErrorCategory.FAILED_EXECUTION,
             target=ErrorTarget.AOAI_GRADER,
         )
diff --git a/sdk/evaluation/azure-ai-evaluation/tests/unittests/test_evaluate_aoai.py b/sdk/evaluation/azure-ai-evaluation/tests/unittests/test_evaluate_aoai.py
index 6b1eab60dd13..dee7b45517b4 100644
--- a/sdk/evaluation/azure-ai-evaluation/tests/unittests/test_evaluate_aoai.py
+++ b/sdk/evaluation/azure-ai-evaluation/tests/unittests/test_evaluate_aoai.py
@@ -1,6 +1,8 @@
 import pytest
 import copy
-from azure.ai.evaluation._evaluate._evaluate_aoai import _combine_item_schemas
+from unittest.mock import MagicMock, patch
+from azure.ai.evaluation._evaluate._evaluate_aoai import _combine_item_schemas, _get_single_run_results
+from azure.ai.evaluation._exceptions import ErrorBlame, EvaluationException
 
 
 @pytest.fixture
@@ -119,3 +121,85 @@ def test_combine_item_schemas_with_external_properties_without_required(self, de
 
         assert data_source_config["item_schema"]["properties"] == expected_properties
         assert data_source_config["item_schema"]["required"] == expected_required
+
+
+class TestGetSingleRunResultsBlame:
+    """Unit tests for blame attribution in _get_single_run_results."""
+
+    def _make_run_info(self, client):
+        return {
+            "client": client,
+            "eval_group_id": "group-1",
+            "eval_run_id": "run-1",
+            "grader_name_map": {},
+        }
+
+    @patch("azure.ai.evaluation._evaluate._evaluate_aoai._wait_for_run_conclusion")
+    @pytest.mark.parametrize("code", ["UserError", "usererror", "USERERROR", "uSeReRrOr"])
+    def test_user_error_code_sets_user_blame(self, mock_wait, code):
+        """When run fails with error.code matching 'usererror' (case-insensitive), blame should be USER_ERROR."""
+        run_result = MagicMock()
+        run_result.status = "failed"
+        run_result.error.code = code
+        mock_wait.return_value = run_result
+        client = MagicMock()
+
+        with pytest.raises(EvaluationException) as exc_info:
+            _get_single_run_results(self._make_run_info(client))
+
+        assert exc_info.value.blame == ErrorBlame.USER_ERROR
+
+    @patch("azure.ai.evaluation._evaluate._evaluate_aoai._wait_for_run_conclusion")
+    def test_non_user_error_code_sets_unknown_blame(self, mock_wait):
+        """When run fails with a non-UserError code, blame should be UNKNOWN."""
+        run_result = MagicMock()
+        run_result.status = "failed"
+        run_result.error.code = "SystemError"
+        mock_wait.return_value = run_result
+        client = MagicMock()
+
+        with pytest.raises(EvaluationException) as exc_info:
+            _get_single_run_results(self._make_run_info(client))
+
+        assert exc_info.value.blame == ErrorBlame.UNKNOWN
+
+    @patch("azure.ai.evaluation._evaluate._evaluate_aoai._wait_for_run_conclusion")
+    def test_missing_error_attribute_sets_unknown_blame(self, mock_wait):
+        """When run fails and error attribute is absent, blame should be UNKNOWN."""
+        run_result = MagicMock(spec=["status"])
+        run_result.status = "failed"
+        mock_wait.return_value = run_result
+        client = MagicMock()
+
+        with pytest.raises(EvaluationException) as exc_info:
+            _get_single_run_results(self._make_run_info(client))
+
+        assert exc_info.value.blame == ErrorBlame.UNKNOWN
+
+    @patch("azure.ai.evaluation._evaluate._evaluate_aoai._wait_for_run_conclusion")
+    def test_error_present_but_code_missing_sets_unknown_blame(self, mock_wait):
+        """When error object exists but has no code attribute, blame should be UNKNOWN."""
+        run_result = MagicMock()
+        run_result.status = "failed"
+        run_result.error = MagicMock(spec=[])  # error object without 'code'
+        mock_wait.return_value = run_result
+        client = MagicMock()
+
+        with pytest.raises(EvaluationException) as exc_info:
+            _get_single_run_results(self._make_run_info(client))
+
+        assert exc_info.value.blame == ErrorBlame.UNKNOWN
+
+    @patch("azure.ai.evaluation._evaluate._evaluate_aoai._wait_for_run_conclusion")
+    def test_error_is_none_sets_unknown_blame(self, mock_wait):
+        """When error attribute is None, blame should be UNKNOWN."""
+        run_result = MagicMock()
+        run_result.status = "failed"
+        run_result.error = None
+        mock_wait.return_value = run_result
+        client = MagicMock()
+
+        with pytest.raises(EvaluationException) as exc_info:
+            _get_single_run_results(self._make_run_info(client))
+
+        assert exc_info.value.blame == ErrorBlame.UNKNOWN