A liquid cooling system includes a heat absorbing unit (4) defining a chamber therein for containing coolant, and a heat dissipation unit (2) comprising a liquid circulation module (20) in flow communication with the heat absorbing unit, and a plurality of cooling fins (27). The liquid circulation module comprises first and second hollow cooling bodies (21, 23) cooperatively defining a space therebetween to receive the cooling fins, and a pump (24) coupled to the second cooling body, so that the first and second cooling bodies, the pump, and the heat absorbing unit together forms a closed loop for circulation of the coolant.