A steering ratio control system of a vehicle includes a variable steering ratio mechanism variably adjusting a steering ratio of a steer angle at left and right steered road wheels to a steering-wheel rotation angle, and a braking/driving force control unit individually controlling braking force and/or driving force of the left and right steered wheels. A steering ratio control unit determines a reference steering ratio based on a vehicle's driving state. The steering ratio control unit calculates a steering-ratio correction value needed for canceling torque steer resulting from a difference in braking force and/or driving force between the left and right steered wheels. A final steering ratio is determined based on both of the reference steering ratio and the steering-ratio correction value to drive the variable steering ratio mechanism responsively to the final steering ratio reflecting the steering-ratio correction value.