diff --git a/aws_lambda_powertools/utilities/idempotency/base.py b/aws_lambda_powertools/utilities/idempotency/base.py
index f93b9097611..f6a3563c103 100644
--- a/aws_lambda_powertools/utilities/idempotency/base.py
+++ b/aws_lambda_powertools/utilities/idempotency/base.py
@@ -60,7 +60,7 @@ def _prepare_data(data: Any) -> Any:
 
     # Convert from Pydantic model
     if callable(getattr(data, "model_dump", None)):
-        return data.model_dump()
+        return data.model_dump(mode="json")
 
     # Convert from event source data class
     if callable(getattr(data, "dict", None)):
diff --git a/tests/functional/idempotency/_pydantic/test_idempotency_pydantic_json_serialization.py b/tests/functional/idempotency/_pydantic/test_idempotency_pydantic_json_serialization.py
new file mode 100644
index 00000000000..624e4239e98
--- /dev/null
+++ b/tests/functional/idempotency/_pydantic/test_idempotency_pydantic_json_serialization.py
@@ -0,0 +1,185 @@
+"""
+Test for issue #8065: @idempotent_function fails with non-JSON-serializable types in Pydantic models
+
+Bug: _prepare_data() calls model_dump() without mode="json", which doesn't
+serialize UUIDs, dates, datetimes, Decimals, and Paths to JSON-compatible strings.
+"""
+
+from datetime import date, datetime
+from decimal import Decimal
+from pathlib import PurePosixPath
+from uuid import UUID
+
+from pydantic import BaseModel
+
+from aws_lambda_powertools.utilities.idempotency import (
+    IdempotencyConfig,
+    idempotent_function,
+)
+from aws_lambda_powertools.utilities.idempotency.persistence.base import (
+    BasePersistenceLayer,
+    DataRecord,
+)
+from tests.functional.idempotency.utils import hash_idempotency_key
+
+TESTS_MODULE_PREFIX = "test-func.tests.functional.idempotency._pydantic.test_idempotency_pydantic_json_serialization"
+
+
+class MockPersistenceLayer(BasePersistenceLayer):
+    def __init__(self, expected_idempotency_key: str):
+        self.expected_idempotency_key = expected_idempotency_key
+        super().__init__()
+
+    def _put_record(self, data_record: DataRecord) -> None:
+        assert data_record.idempotency_key == self.expected_idempotency_key
+
+    def _update_record(self, data_record: DataRecord) -> None:
+        assert data_record.idempotency_key == self.expected_idempotency_key
+
+    def _get_record(self, idempotency_key) -> DataRecord: ...
+
+    def _delete_record(self, data_record: DataRecord) -> None: ...
+
+
+# --- Models ---
+
+
+class PaymentWithUUID(BaseModel):
+    payment_id: UUID
+    customer_id: str
+
+
+class EventWithDate(BaseModel):
+    event_id: str
+    event_date: date
+
+
+class OrderWithDatetime(BaseModel):
+    order_id: str
+    created_at: datetime
+
+
+class InvoiceWithDecimal(BaseModel):
+    invoice_id: str
+    amount: Decimal
+
+
+class ConfigWithPath(BaseModel):
+    config_id: str
+    file_path: PurePosixPath
+
+
+def test_idempotent_function_with_uuid():
+    # GIVEN
+    config = IdempotencyConfig(use_local_cache=True)
+    payment_uuid = UUID("12345678-1234-5678-1234-567812345678")
+    mock_event = {"payment_id": str(payment_uuid), "customer_id": "c-456"}
+    idempotency_key = f"{TESTS_MODULE_PREFIX}.test_idempotent_function_with_uuid.<locals>.collect_payment#{hash_idempotency_key(mock_event)}"  # noqa E501
+    persistence_layer = MockPersistenceLayer(expected_idempotency_key=idempotency_key)
+
+    @idempotent_function(
+        data_keyword_argument="payment",
+        persistence_store=persistence_layer,
+        config=config,
+    )
+    def collect_payment(payment: PaymentWithUUID) -> dict:
+        return {"status": "ok"}
+
+    # WHEN
+    payment = PaymentWithUUID(payment_id=payment_uuid, customer_id="c-456")
+    result = collect_payment(payment=payment)
+
+    # THEN
+    assert result == {"status": "ok"}
+
+
+def test_idempotent_function_with_date():
+    # GIVEN
+    config = IdempotencyConfig(use_local_cache=True)
+    mock_event = {"event_id": "evt-001", "event_date": "2024-03-20"}
+    idempotency_key = f"{TESTS_MODULE_PREFIX}.test_idempotent_function_with_date.<locals>.process_event#{hash_idempotency_key(mock_event)}"  # noqa E501
+    persistence_layer = MockPersistenceLayer(expected_idempotency_key=idempotency_key)
+
+    @idempotent_function(
+        data_keyword_argument="event",
+        persistence_store=persistence_layer,
+        config=config,
+    )
+    def process_event(event: EventWithDate) -> dict:
+        return {"status": "ok"}
+
+    # WHEN
+    event = EventWithDate(event_id="evt-001", event_date=date(2024, 3, 20))
+    result = process_event(event=event)
+
+    # THEN
+    assert result == {"status": "ok"}
+
+
+def test_idempotent_function_with_datetime():
+    # GIVEN
+    config = IdempotencyConfig(use_local_cache=True)
+    mock_event = {"order_id": "ord-001", "created_at": "2024-03-20T14:30:00"}
+    idempotency_key = f"{TESTS_MODULE_PREFIX}.test_idempotent_function_with_datetime.<locals>.process_order#{hash_idempotency_key(mock_event)}"  # noqa E501
+    persistence_layer = MockPersistenceLayer(expected_idempotency_key=idempotency_key)
+
+    @idempotent_function(
+        data_keyword_argument="order",
+        persistence_store=persistence_layer,
+        config=config,
+    )
+    def process_order(order: OrderWithDatetime) -> dict:
+        return {"status": "ok"}
+
+    # WHEN
+    order = OrderWithDatetime(order_id="ord-001", created_at=datetime(2024, 3, 20, 14, 30, 0))
+    result = process_order(order=order)
+
+    # THEN
+    assert result == {"status": "ok"}
+
+
+def test_idempotent_function_with_decimal():
+    # GIVEN
+    config = IdempotencyConfig(use_local_cache=True)
+    mock_event = {"invoice_id": "inv-001", "amount": "199.99"}
+    idempotency_key = f"{TESTS_MODULE_PREFIX}.test_idempotent_function_with_decimal.<locals>.process_invoice#{hash_idempotency_key(mock_event)}"  # noqa E501
+    persistence_layer = MockPersistenceLayer(expected_idempotency_key=idempotency_key)
+
+    @idempotent_function(
+        data_keyword_argument="invoice",
+        persistence_store=persistence_layer,
+        config=config,
+    )
+    def process_invoice(invoice: InvoiceWithDecimal) -> dict:
+        return {"status": "ok"}
+
+    # WHEN
+    invoice = InvoiceWithDecimal(invoice_id="inv-001", amount=Decimal("199.99"))
+    result = process_invoice(invoice=invoice)
+
+    # THEN
+    assert result == {"status": "ok"}
+
+
+def test_idempotent_function_with_path():
+    # GIVEN
+    config = IdempotencyConfig(use_local_cache=True)
+    mock_event = {"config_id": "cfg-001", "file_path": "/etc/app/config.yaml"}
+    idempotency_key = f"{TESTS_MODULE_PREFIX}.test_idempotent_function_with_path.<locals>.process_config#{hash_idempotency_key(mock_event)}"  # noqa E501
+    persistence_layer = MockPersistenceLayer(expected_idempotency_key=idempotency_key)
+
+    @idempotent_function(
+        data_keyword_argument="config",
+        persistence_store=persistence_layer,
+        config=config,
+    )
+    def process_config(config: ConfigWithPath) -> dict:
+        return {"status": "ok"}
+
+    # WHEN
+    cfg = ConfigWithPath(config_id="cfg-001", file_path=PurePosixPath("/etc/app/config.yaml"))
+    result = process_config(config=cfg)
+
+    # THEN
+    assert result == {"status": "ok"}