diff --git a/mindsdb/integrations/utilities/rag/rerankers/base_reranker.py b/mindsdb/integrations/utilities/rag/rerankers/base_reranker.py
index 1af4438887..c84b3fa461 100644
--- a/mindsdb/integrations/utilities/rag/rerankers/base_reranker.py
+++ b/mindsdb/integrations/utilities/rag/rerankers/base_reranker.py
@@ -113,7 +113,14 @@ def _init_client(self):
                 if not openai_api_key:
                     raise ValueError(f"OpenAI API key not found in environment variable {api_key_var}")
 
-                base_url = self.base_url or DEFAULT_LLM_ENDPOINT
+                # For Ollama, the default endpoint is the local Ollama server, not OpenAI.
+                # Fall back to provider-specific defaults so that users who omit base_url
+                # get a working configuration out of the box. Fixes gh-11952.
+                if self.provider == 'ollama':
+                    default_base_url = 'http://localhost:11434/v1'
+                else:
+                    default_base_url = DEFAULT_LLM_ENDPOINT
+                base_url = self.base_url or default_base_url
                 self.client = AsyncOpenAI(
                     api_key=openai_api_key, base_url=base_url, timeout=self.request_timeout, max_retries=2
                 )
diff --git a/tests/unit/interfaces/knowledge_base/test_reranker_base_url.py b/tests/unit/interfaces/knowledge_base/test_reranker_base_url.py
new file mode 100644
index 0000000000..a63f22d0ab
--- /dev/null
+++ b/tests/unit/interfaces/knowledge_base/test_reranker_base_url.py
@@ -0,0 +1,97 @@
+"""Tests for BaseLLMReranker provider-specific default base_url (gh-11952).
+
+When the Ollama provider is configured without an explicit base_url, the
+fallback must be http://localhost:11434/v1 — not the OpenAI endpoint.
+Before the fix, all Ollama reranker calls silently hit api.openai.com/v1
+and failed with 404.
+"""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from mindsdb.integrations.utilities.rag.settings import DEFAULT_LLM_ENDPOINT
+from mindsdb.integrations.utilities.rag.rerankers.base_reranker import BaseLLMReranker
+
+OLLAMA_DEFAULT_BASE_URL = "http://localhost:11434/v1"
+
+
+def _make_reranker(**kwargs):
+    """Construct a BaseLLMReranker with _init_client bypassed."""
+    with patch.object(BaseLLMReranker, "_init_client", return_value=None):
+        obj = BaseLLMReranker(**kwargs)
+    return obj
+
+
+class TestOllamaDefaultBaseUrl:
+    """The client must be created with the Ollama-specific URL when base_url is omitted."""
+
+    def test_ollama_without_base_url_uses_ollama_default(self):
+        reranker = _make_reranker(provider="ollama", model="llama3.2", api_key="n/a")
+        reranker.client = None  # force re-init
+
+        with patch(
+            "mindsdb.integrations.utilities.rag.rerankers.base_reranker.AsyncOpenAI"
+        ) as mock_openai:
+            reranker._init_client()
+
+        _, kwargs = mock_openai.call_args
+        assert kwargs.get("base_url") == OLLAMA_DEFAULT_BASE_URL, (
+            f"Expected Ollama default {OLLAMA_DEFAULT_BASE_URL!r}, got {kwargs.get('base_url')!r}. "
+            "Without this fix, Ollama reranker requests hit the OpenAI endpoint and fail with 404."
+        )
+
+    def test_ollama_with_explicit_base_url_respects_it(self):
+        custom_url = "http://my-ollama-server:11434/v1"
+        reranker = _make_reranker(provider="ollama", model="llama3.2", api_key="n/a", base_url=custom_url)
+        reranker.client = None
+
+        with patch(
+            "mindsdb.integrations.utilities.rag.rerankers.base_reranker.AsyncOpenAI"
+        ) as mock_openai:
+            reranker._init_client()
+
+        _, kwargs = mock_openai.call_args
+        assert kwargs.get("base_url") == custom_url
+
+    def test_openai_without_base_url_keeps_openai_default(self):
+        reranker = _make_reranker(provider="openai", model="gpt-4o", api_key="sk-test")
+        reranker.client = None
+
+        with patch(
+            "mindsdb.integrations.utilities.rag.rerankers.base_reranker.AsyncOpenAI"
+        ) as mock_openai:
+            reranker._init_client()
+
+        _, kwargs = mock_openai.call_args
+        assert kwargs.get("base_url") == DEFAULT_LLM_ENDPOINT, (
+            "OpenAI provider without explicit base_url must still default to DEFAULT_LLM_ENDPOINT."
+        )
+
+    def test_openai_with_explicit_base_url_respects_it(self):
+        custom_url = "https://my-openai-proxy.example.com/v1"
+        reranker = _make_reranker(provider="openai", model="gpt-4o", api_key="sk-test", base_url=custom_url)
+        reranker.client = None
+
+        with patch(
+            "mindsdb.integrations.utilities.rag.rerankers.base_reranker.AsyncOpenAI"
+        ) as mock_openai:
+            reranker._init_client()
+
+        _, kwargs = mock_openai.call_args
+        assert kwargs.get("base_url") == custom_url
+
+    def test_ollama_default_is_not_openai_endpoint(self):
+        """Regression: Ollama default must not be the OpenAI endpoint."""
+        reranker = _make_reranker(provider="ollama", model="llama3.2", api_key="n/a")
+        reranker.client = None
+
+        with patch(
+            "mindsdb.integrations.utilities.rag.rerankers.base_reranker.AsyncOpenAI"
+        ) as mock_openai:
+            reranker._init_client()
+
+        _, kwargs = mock_openai.call_args
+        assert kwargs.get("base_url") != DEFAULT_LLM_ENDPOINT, (
+            "Ollama default base_url must not be the OpenAI API endpoint."
+        )