A cooling system of an electric vehicle is provided. The system includes an integral valve having at least one or more coolant inlets and at least two or more coolant outlets, and selectively discharges a coolant through one of the at least two or more coolant outlets. A plurality of coolant paths connected such that the coolant discharged through one of the at least two or more coolant outlets is introduced back into the integral valve through the at least one or more coolant inlets after being supplied to a portion where coolant circulation is required. A heat pump device is disposed in at least one or more of the plurality of coolant paths to selectively increase or decrease a temperature of the coolant.