A steering angle ratio control system is provided which includes a steering angle ratio varying mechanism capable of varying a steering angle ratio by an electric drive unit, and a controller for controlling the steering angle ratio varying mechanism based on a steering angle ratio determined by a steering angle ratio determining section. The controller includes an electric drive unit overheat protecting section that determines, when the temperature of the electric drive unit rises beyond a predetermined temperature, a smaller steering angle ratio as compared with a steering angle ratio determined thereby when the temperature of the electric drive unit is lower than the predetermined temperature. A steering angle ratio control method is also provided.