In an outboard motor steering control system having a plurality of outboard motors each mounted on a stern of a boat by a shaft to be movable by an outboard motor actuator relative to the boat and each having an internal combustion engine and a propeller powered by the engine to propel the boat, a tie-bar motor (actuator) is operated such that the outboard motors can be finely operated synchronously to make desired steering angles finely, i.e., to achieve the desired steering angles in response to a detected rotation angle of a steering wheel. Also outboard motor actuators are individually operated to regulate the relative angles between the outboard motors, thereby enhancing both straight course-holding performance and turning performance.