Disclosed herein is a pulsation damping device of a hydraulic brake system. The pulsation damping device of a hydraulic brake system which attenuates a pressure pulsation of brake oil discharged from a pump comprise a sleeve inserted into a bore which communicates with an inport into which the brake oil is introduced and an outport through which the brake oil is discharged, wherein one end of the sleeve is open and the other end is closed, a damping member accommodated in the sleeve and hollowed to form a damping space therein, and a stopper member configured to block one open end of the bore and coupled to an opening of the sleeve.