An electronic brake system and a method for operating the same are disclosed. The electronic brake system includes an integrated master cylinder, a hydraulic-pressure supply device, and a hydraulic control unit. The integrated master cylinder allows a brake fluid to be discharged based on displacement of a brake pedal and at the same time provides proper pedal feel for the user. The hydraulic-pressure supply device generates hydraulic pressure by operating a hydraulic piston in response to an electrical signal that is output in response to displacement of the brake pedal. The hydraulic control unit controls hydraulic pressure of brake fluid supplied to respective wheel cylinders. The electronic brake system operates in different ways according to a normal operation mode and an abnormal operation mode.