In a rear wheel steering control system for a vehicle, a rear wheel steering control unit (53) forces the toe angle of each rear wheel (3rl, 3rr) to a substantially neutral position or a slightly toe-in position when a road condition estimating unit (63) has detected a rough road surface. Thereby, when the vehicle is traveling over a rough road surface, the actuator is forced to the neutral position, and the rear wheels are brought to a neutral position so that the changes in the wheel geometry (tread and/or alignment) of the rear wheels at the time of a bump or a rebound can be avoided. Therefore, the ride quality of a vehicle equipped with the rear wheel steering control system is favorably maintained even when the vehicle is traveling over a road surface, and the rear wheels undergo large vertical displacements.