diff --git a/src/adapters/base.py b/src/adapters/base.py
index c54d517..972c670 100644
--- a/src/adapters/base.py
+++ b/src/adapters/base.py
@@ -2,6 +2,7 @@
 from abc import ABC, abstractmethod
 
 from domain.stock import CreateStock, Stock
+from domain.portfolio import Portfolio
 
 
 class AbstractStockRepository(ABC):
@@ -9,5 +10,12 @@ class AbstractStockRepository(ABC):
     def create(self, stock: CreateStock) -> str:
         """Create a new stock entry in the repository."""
 
+    @abstractmethod
     def list(self, user_id: int) -> List[Stock]:
         """List all stock by user id"""
+
+
+class AbstractPortfolioRepository(ABC):
+    @abstractmethod
+    def update(self, portfolio: Portfolio) -> None:
+        """Update portfolio in the repository"""
diff --git a/src/adapters/portfolio.py b/src/adapters/portfolio.py
new file mode 100644
index 0000000..b5582d8
--- /dev/null
+++ b/src/adapters/portfolio.py
@@ -0,0 +1,20 @@
+from dataclasses import asdict
+from datetime import datetime, timezone
+from pymongo import MongoClient
+from pymongo.database import Database
+from .base import AbstractPortfolioRepository
+from domain.portfolio import Portfolio
+
+
+class PortfolioRepository(AbstractPortfolioRepository):
+    def __init__(self, mongo_client: MongoClient, database_name: str = "stock_db"):
+        self.client = mongo_client
+        self.db: Database = self.client[database_name]
+        self.collection = self.db["portfolio"]
+
+    def update(self, portfolio: Portfolio) -> None:
+        portfolio.updated_at = datetime.now(timezone.utc)
+        self.collection.replace_one({"user_id": portfolio.user_id}, asdict(portfolio), upsert=True)
+
+    def __del__(self):
+        self.client.close()
diff --git a/src/domain/portfolio.py b/src/domain/portfolio.py
new file mode 100644
index 0000000..b1d6610
--- /dev/null
+++ b/src/domain/portfolio.py
@@ -0,0 +1,20 @@
+from dataclasses import dataclass
+from datetime import datetime
+from typing import List
+
+
+@dataclass
+class Holding:
+    symbol: str
+    shares: int
+    total_cost: float
+
+
+@dataclass
+class Portfolio:
+    user_id: int
+    cash_balance: float
+    total_money_in: float
+    holdings: List[Holding]
+    created_at: datetime
+    updated_at: datetime
diff --git a/src/tests/test_portfolio_adapters.py b/src/tests/test_portfolio_adapters.py
new file mode 100644
index 0000000..7148a62
--- /dev/null
+++ b/src/tests/test_portfolio_adapters.py
@@ -0,0 +1,86 @@
+import pytest
+from datetime import datetime, timezone
+from dataclasses import asdict
+from pymongo import MongoClient
+from domain.portfolio import Portfolio, Holding
+from adapters.portfolio import PortfolioRepository
+
+
+@pytest.fixture(scope="module")
+def mongo_client():
+    client = MongoClient("mongodb://localhost:27015")
+    yield client
+    client.drop_database("test_stock_db")
+    client.close()
+
+
+@pytest.fixture(scope="module")
+def portfolio_repository(mongo_client):
+    return PortfolioRepository(mongo_client, database_name="test_stock_db")
+
+
+@pytest.fixture(scope="function", autouse=True)
+def clear_collection(portfolio_repository):
+    portfolio_repository.collection.delete_many({})
+
+
+class TestPortfolioRepository:
+    def test_update_new_portfolio(self, portfolio_repository):
+        # Arrange
+        created_at = datetime.now(timezone.utc)
+        portfolio = Portfolio(
+            user_id=1,
+            cash_balance=1000.0,
+            total_money_in=1000.0,
+            holdings=[Holding(symbol="AAPL", shares=10, total_cost=1500.0)],
+            created_at=created_at,
+            updated_at=created_at,
+        )
+
+        # Action
+        portfolio_repository.update(portfolio)
+
+        # Assertion
+        result = portfolio_repository.collection.find_one({"user_id": 1})
+        assert result["user_id"] == portfolio.user_id
+        assert result["cash_balance"] == portfolio.cash_balance
+        assert result["total_money_in"] == portfolio.total_money_in
+        assert len(result["holdings"]) == 1
+        assert result["holdings"][0]["symbol"] == "AAPL"
+        assert result["holdings"][0]["shares"] == 10
+        assert result["holdings"][0]["total_cost"] == 1500.0
+
+    def test_update_existing_portfolio(self, portfolio_repository):
+        # Arrange
+        initial_portfolio = Portfolio(
+            user_id=1,
+            cash_balance=1000.0,
+            total_money_in=1000.0,
+            holdings=[Holding(symbol="AAPL", shares=10, total_cost=1500.0)],
+            created_at=datetime.now(timezone.utc),
+            updated_at=datetime.now(timezone.utc),
+        )
+        result = portfolio_repository.collection.insert_one(asdict(initial_portfolio))
+
+        updated_portfolio = Portfolio(
+            user_id=1,
+            cash_balance=2000.0,
+            total_money_in=2000.0,
+            holdings=[Holding(symbol="AAPL", shares=20, total_cost=3000.0)],
+            created_at=initial_portfolio.created_at,
+            updated_at=datetime.now(timezone.utc),
+        )
+
+        # Action
+        portfolio_repository.update(updated_portfolio)
+
+        # Assertion
+        result = portfolio_repository.collection.find_one({"user_id": 1})
+        assert result is not None
+        assert result["user_id"] == updated_portfolio.user_id
+        assert result["cash_balance"] == 2000.0
+        assert result["total_money_in"] == 2000.0
+        assert len(result["holdings"]) == 1
+        assert result["holdings"][0]["symbol"] == "AAPL"
+        assert result["holdings"][0]["shares"] == 20
+        assert result["holdings"][0]["total_cost"] == 3000.0