A lane departure control system is provided which works to control a lane departure of a vehicle using a steering mechanism. The lane departure control system determines a deviation angle between a direction in which the vehicle is pointing and a boundary line of a lane. When the vehicle is expected to unintentionally leave the lane, the lane departure control system calculates an assist angle between a target angular direction of the vehicle and the boundary line and outputs a control signal to the steering mechanism to steer the vehicle in a direction away from the boundary line toward the center of the lane by the sum of the deviation angle and the assist angle. The lane departure control system determines the assist angle as a function of the deviation angle. Such calculation results in a decreased load on the system in controlling the steering of the vehicle.
