In an outboard motor steering control system having a plurality of outboard motors each adapted to be mounted on a stern of a boat by a shaft to be movable by an actuator relative to the boat and each having an internal combustion engine to power a propeller, a desired steering angle of each outboard motor is determined individually based on detected engine speed and rotation angle of a steering wheel, and the operation of the actuator is controlled based on the determined desired steering angle, thereby improving both straight course-holding performance and turning performance by regulating the relative angles between the outboard motors in response to the cruising conditions of the boat.