A vehicle steering system for steering vehicle wheels includes a steering wheel, a steering power assisting unit for providing assisting power when the steering wheel is steered, a transfer ratio control mechanism for controlling the ratio of a steering angle of the steering wheel to a steered angle of the vehicle wheels according to a vehicle condition; a steering torque sensor, a motor control circuit for controlling the driving motor so as to cancel the steering torque applied to the steering wheel when the steering torque sensor detects a steering torque applied to the steering wheel until the transfer ratio control mechanism starts operation. The transfer ratio control mechanism includes a transfer ratio changing mechanism and a driving motor for driving the transfer ratio changing mechanism.