A vehicle steering system, including: a steering actuator including an electric motor, a steering rod configured to steer a wheel by a steering amount, and a motion converting mechanism configured to convert a rotating motion of a motor rotation shaft into a motion of the steering rod; first and second motor rotation angle sensors configured to detect a motor rotation angle; a steering amount sensor configured to detect a motion amount of the steering rod as the steering amount; and a controller configured to execute a steering amount control and to perform detection-value inappropriateness determination in which it is determined that any one or two of a detection value of the first motor rotation angle sensor, a detection value of the second motor rotation angle sensor, and a detection value of the steering amount sensor are inappropriate based on comparison among the detection values.