diff --git a/src/google/adk/evaluation/in_memory_eval_sets_manager.py b/src/google/adk/evaluation/in_memory_eval_sets_manager.py
new file mode 100644
index 00000000..dbad8db5
--- /dev/null
+++ b/src/google/adk/evaluation/in_memory_eval_sets_manager.py
@@ -0,0 +1,151 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import annotations
+
+import time
+from typing import Optional
+
+from typing_extensions import override
+
+from ..errors.not_found_error import NotFoundError
+from .eval_case import EvalCase
+from .eval_set import EvalSet
+from .eval_sets_manager import EvalSetsManager
+
+
+class InMemoryEvalSetsManager(EvalSetsManager):
+  """An in-memory implementation of EvalSetsManager using dictionaries.
+
+  You can use this class:
+  1) As a part of your testcase.
+  2) For cases where other implementations of EvalSetsManager are too expensive
+  to use.
+  """
+
+  def __init__(self):
+    # {app_name: {eval_set_id: EvalSet}}
+    self._eval_sets: dict[str, dict[str, EvalSet]] = {}
+    # {app_name: {eval_set_id: {eval_case_id: EvalCase}}}
+    self._eval_cases: dict[str, dict[str, dict[str, EvalCase]]] = {}
+
+  def _ensure_app_exists(self, app_name: str):
+    if app_name not in self._eval_sets:
+      self._eval_sets[app_name] = {}
+      self._eval_cases[app_name] = {}
+
+  @override
+  def get_eval_set(self, app_name: str, eval_set_id: str) -> Optional[EvalSet]:
+    self._ensure_app_exists(app_name)
+    return self._eval_sets[app_name].get(eval_set_id, None)
+
+  @override
+  def create_eval_set(self, app_name: str, eval_set_id: str):
+    self._ensure_app_exists(app_name)
+    if eval_set_id in self._eval_sets[app_name]:
+      raise ValueError(
+          f"EvalSet {eval_set_id} already exists for app {app_name}."
+      )
+
+    new_eval_set = EvalSet(
+        eval_set_id=eval_set_id,
+        eval_cases=[],
+        creation_timestamp=time.time(),
+    )
+    self._eval_sets[app_name][eval_set_id] = new_eval_set
+    self._eval_cases[app_name][eval_set_id] = {}
+
+  @override
+  def list_eval_sets(self, app_name: str) -> list[str]:
+    if app_name not in self._eval_sets:
+      return []
+
+    return list(self._eval_sets[app_name].keys())
+
+  @override
+  def get_eval_case(
+      self, app_name: str, eval_set_id: str, eval_case_id: str
+  ) -> Optional[EvalCase]:
+    if app_name not in self._eval_cases:
+      return None
+    if eval_set_id not in self._eval_cases[app_name]:
+      return None
+    return self._eval_cases[app_name][eval_set_id].get(eval_case_id)
+
+  @override
+  def add_eval_case(self, app_name: str, eval_set_id: str, eval_case: EvalCase):
+    self._ensure_app_exists(app_name)
+    if eval_set_id not in self._eval_sets[app_name]:
+      raise NotFoundError(
+          f"EvalSet {eval_set_id} not found for app {app_name}."
+      )
+    if eval_case.eval_id in self._eval_cases[app_name][eval_set_id]:
+      raise ValueError(
+          f"EvalCase {eval_case.eval_id} already exists in EvalSet"
+          f" {eval_set_id} for app {app_name}."
+      )
+
+    self._eval_cases[app_name][eval_set_id][eval_case.eval_id] = eval_case
+    # Also update the list in the EvalSet object
+    self._eval_sets[app_name][eval_set_id].eval_cases.append(eval_case)
+
+  @override
+  def update_eval_case(
+      self, app_name: str, eval_set_id: str, updated_eval_case: EvalCase
+  ):
+    self._ensure_app_exists(app_name)
+    if eval_set_id not in self._eval_sets[app_name]:
+      raise NotFoundError(
+          f"EvalSet {eval_set_id} not found for app {app_name}."
+      )
+    if updated_eval_case.eval_id not in self._eval_cases[app_name][eval_set_id]:
+      raise NotFoundError(
+          f"EvalCase {updated_eval_case.eval_id} not found in EvalSet"
+          f" {eval_set_id} for app {app_name}."
+      )
+
+    # Full replace
+    self._eval_cases[app_name][eval_set_id][
+        updated_eval_case.eval_id
+    ] = updated_eval_case
+
+    # Update the list in the EvalSet object
+    eval_set = self._eval_sets[app_name][eval_set_id]
+    for i, case in enumerate(eval_set.eval_cases):
+      if case.eval_id == updated_eval_case.eval_id:
+        eval_set.eval_cases[i] = updated_eval_case
+        break
+
+  @override
+  def delete_eval_case(
+      self, app_name: str, eval_set_id: str, eval_case_id: str
+  ):
+    self._ensure_app_exists(app_name)
+    if eval_set_id not in self._eval_sets[app_name]:
+      raise NotFoundError(
+          f"EvalSet {eval_set_id} not found for app {app_name}."
+      )
+    if eval_case_id not in self._eval_cases[app_name][eval_set_id]:
+      raise NotFoundError(
+          f"EvalCase {eval_case_id} not found in EvalSet {eval_set_id}"
+          f" for app {app_name}."
+      )
+
+    del self._eval_cases[app_name][eval_set_id][eval_case_id]
+
+    # Remove from the list in the EvalSet object
+    eval_set = self._eval_sets[app_name][eval_set_id]
+    eval_set.eval_cases = [
+        case for case in eval_set.eval_cases if case.eval_id != eval_case_id
+    ]
diff --git a/tests/unittests/evaluation/test_in_memory_eval_sets_manager.py b/tests/unittests/evaluation/test_in_memory_eval_sets_manager.py
new file mode 100644
index 00000000..dc1078dc
--- /dev/null
+++ b/tests/unittests/evaluation/test_in_memory_eval_sets_manager.py
@@ -0,0 +1,199 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import time
+
+from google.adk.errors.not_found_error import NotFoundError
+from google.adk.evaluation.eval_case import EvalCase
+from google.adk.evaluation.in_memory_eval_sets_manager import InMemoryEvalSetsManager
+import pytest
+
+
+@pytest.fixture
+def app_name():
+  return "test_app"
+
+
+@pytest.fixture
+def manager():
+  return InMemoryEvalSetsManager()
+
+
+@pytest.fixture
+def eval_set_id():
+  return "test_eval_set"
+
+
+@pytest.fixture
+def eval_case_id():
+  return "test_eval_case"
+
+
+def test_create_eval_set(manager, app_name, eval_set_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_set = manager.get_eval_set(app_name, eval_set_id)
+  assert eval_set is not None
+  assert eval_set.eval_set_id == eval_set_id
+  assert eval_set.eval_cases == []
+
+
+def test_create_eval_set_already_exists(manager, app_name, eval_set_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  with pytest.raises(ValueError):
+    manager.create_eval_set(app_name, eval_set_id)
+
+
+def test_get_eval_set(manager, app_name, eval_set_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_set = manager.get_eval_set(app_name, eval_set_id)
+  assert eval_set is not None
+  assert eval_set.eval_set_id == eval_set_id
+
+
+def test_get_eval_set_not_found(manager, app_name):
+  eval_set = manager.get_eval_set(app_name, "nonexistent_set")
+  assert eval_set is None
+
+
+def test_get_eval_set_wrong_app(manager, app_name, eval_set_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_set = manager.get_eval_set("wrong_app", eval_set_id)
+  assert eval_set is None
+
+
+def test_list_eval_sets(manager, app_name):
+  manager.create_eval_set(app_name, "set1")
+  manager.create_eval_set(app_name, "set2")
+  eval_sets = manager.list_eval_sets(app_name)
+  assert len(eval_sets) == 2
+  assert "set1" in eval_sets
+  assert "set2" in eval_sets
+
+
+def test_list_eval_sets_wrong_app(manager, app_name):
+  manager.create_eval_set(app_name, "set1")
+  eval_sets = manager.list_eval_sets("wrong_app")
+  assert len(eval_sets) == 0
+
+
+def test_add_eval_case(manager, app_name, eval_set_id, eval_case_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_case = EvalCase(eval_id=eval_case_id, conversation=[])
+  manager.add_eval_case(app_name, eval_set_id, eval_case)
+
+  retrieved_case = manager.get_eval_case(app_name, eval_set_id, eval_case_id)
+  assert retrieved_case is not None
+  assert retrieved_case.eval_id == eval_case_id
+
+  eval_set = manager.get_eval_set(app_name, eval_set_id)
+  assert len(eval_set.eval_cases) == 1
+  assert eval_set.eval_cases[0].eval_id == eval_case_id
+
+
+def test_add_eval_case_set_not_found(
+    manager, app_name, eval_set_id, eval_case_id
+):
+  eval_case = EvalCase(eval_id=eval_case_id, conversation=[])
+  with pytest.raises(NotFoundError):
+    manager.add_eval_case(app_name, eval_set_id, eval_case)
+
+
+def test_add_eval_case_already_exists(
+    manager, app_name, eval_set_id, eval_case_id
+):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_case = EvalCase(eval_id=eval_case_id, conversation=[])
+  manager.add_eval_case(app_name, eval_set_id, eval_case)
+  with pytest.raises(ValueError):
+    manager.add_eval_case(app_name, eval_set_id, eval_case)
+
+
+def test_get_eval_case(manager, app_name, eval_set_id, eval_case_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_case = EvalCase(eval_id=eval_case_id, conversation=[])
+  manager.add_eval_case(app_name, eval_set_id, eval_case)
+  retrieved_case = manager.get_eval_case(app_name, eval_set_id, eval_case_id)
+  assert retrieved_case is not None
+  assert retrieved_case.eval_id == eval_case_id
+
+
+def test_get_eval_case_not_found(manager, app_name, eval_set_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  retrieved_case = manager.get_eval_case(
+      app_name, eval_set_id, "nonexistent_case"
+  )
+  assert retrieved_case is None
+
+
+def test_get_eval_case_set_not_found(manager, app_name, eval_case_id):
+  retrieved_case = manager.get_eval_case(
+      app_name, "nonexistent_set", eval_case_id
+  )
+  assert retrieved_case is None
+
+
+def test_update_eval_case(manager, app_name, eval_set_id, eval_case_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_case = EvalCase(eval_id=eval_case_id, conversation=[])
+  manager.add_eval_case(app_name, eval_set_id, eval_case)
+
+  updated_eval_case = EvalCase(
+      eval_id=eval_case_id, conversation=[], creation_timestamp=time.time()
+  )
+  manager.update_eval_case(app_name, eval_set_id, updated_eval_case)
+
+  retrieved_case = manager.get_eval_case(app_name, eval_set_id, eval_case_id)
+  assert retrieved_case is not None
+  assert retrieved_case.creation_timestamp != 0.0
+  assert (
+      retrieved_case.creation_timestamp == updated_eval_case.creation_timestamp
+  )
+
+  eval_set = manager.get_eval_set(app_name, eval_set_id)
+  assert len(eval_set.eval_cases) == 1
+  assert (
+      eval_set.eval_cases[0].creation_timestamp
+      == updated_eval_case.creation_timestamp
+  )
+
+
+def test_update_eval_case_not_found(
+    manager, app_name, eval_set_id, eval_case_id
+):
+  manager.create_eval_set(app_name, eval_set_id)
+  updated_eval_case = EvalCase(eval_id=eval_case_id, conversation=[])
+  with pytest.raises(NotFoundError):
+    manager.update_eval_case(app_name, eval_set_id, updated_eval_case)
+
+
+def test_delete_eval_case(manager, app_name, eval_set_id, eval_case_id):
+  manager.create_eval_set(app_name, eval_set_id)
+  eval_case = EvalCase(eval_id=eval_case_id, conversation=[])
+  manager.add_eval_case(app_name, eval_set_id, eval_case)
+
+  manager.delete_eval_case(app_name, eval_set_id, eval_case_id)
+
+  retrieved_case = manager.get_eval_case(app_name, eval_set_id, eval_case_id)
+  assert retrieved_case is None
+
+  eval_set = manager.get_eval_set(app_name, eval_set_id)
+  assert len(eval_set.eval_cases) == 0
+
+
+def test_delete_eval_case_not_found(
+    manager, app_name, eval_set_id, eval_case_id
+):
+  manager.create_eval_set(app_name, eval_set_id)
+  with pytest.raises(NotFoundError):
+    manager.delete_eval_case(app_name, eval_set_id, eval_case_id)