A portable computer and a locking mechanism thereof are provided. The portable computer includes a battery, a host and a locking mechanism. The battery has a locking hole. The battery includes a restraining protrusion. The host has a receiving through. The locking mechanism is disposed in the receiving through. The locking mechanism includes a main body and a locking protrusion. The main body has a first restraining concave and a second restraining concave. The locking protrusion is connected to the main body. When the restraining protrusion is placed in the first restraining concave, the locking protrusion is locked in the locking hole, so that the battery is locked in the receiving through. When the restraining protrusion is placed in the second restraining concave, the locking protrusion leaves the locking hole, so that the battery is dismounted from the receiving through.