A system for controlling steering of a vehicle, including a steering unit having an electric motor which steers driven wheels of the vehicle, a first steering control unit (EPS ECU 76) for controlling the actuator, a CCD camera for detecting a condition of a lane on a road on which the vehicle travels, a steering assist torque determining unit for determining a steering assist torque necessary for holding a positional relationship between the vehicle and the lane condition, a torque sensor for detecting a steering torque manually applied to the steering unit by the driver, second steering control unit for calculating a torque command to be output to the first steering control unit based on the steering assist torque calculated by the steering assist torque calculating unit and the detected steering torque to control the motor such that the torque command decreases. In the system, a failure detecting unit is provided for detecting whether a failure has occurred at least in determination of the steering assist torque, and the control by the second control unit is discontinued, or is switched to the control by the first control unit when the failure is detected, thereby enabling to detect or discriminate the occurrence of failure with accuracy and to take a necessary countermeasure to cope with the failures condition.