A brake control system includes a master cylinder to produce a master cylinder pressure, a brake booster to assist the master cylinder, a first control unit to control the booster, a hydraulic modulator to supply a wheel cylinder pressure to a wheel cylinder, and a second control unit to control the hydraulic modulator. The hydraulic modulator includes a pressure source, such as a pump, to increase the wheel cylinder pressure. The first and second control units are connected together by a communication line. The brake control system may further include a boost condition transmitting section to transmit, through the communicating line, a condition of a boost system formed by the brake booster and the first control unit.