A liquid cooling system includes a cooling body (1) defining an hollow portion receiving a pump (3) and a number of cooling fins (18) therein, and a contact portion for contacting an electrical component. The cooling body defines a passageway therein filled with liquid coolant, and an inlet (124) and an outlet (125) both in communication with the passageway. The pump defines an exit (31) and an entrance (32) connected to the inlet and the outlet of the cooling body respectively by two tubes (5). Heat is transferred from the electrical component to the contact portion, and then conducted to the coolant, and conducted to other portions of the cooling body as the coolant flows through the passageway. The heat is then conducted to the cooling fins for dissipation.