Abstract: A slope mower includes a mower body, drive wheels, left and right mower decks and left and right support wheels mounted on support arms pivotally mounted to the mower body with hydraulic actuators acting on the left and right support arms to maintain the mower body vertical. An inclinometer measures the tilt angle of the mower body and a controller reads the angle and controls a leveling valve to supply hydraulic fluid from a supply line to the leveling actuator toward which the inclinometer indicates the mower body is leaning to move the mower body back to vertical. The system can be programmed to actuate a leveling actuator only when the detected tilt angle exceeds a minimum angle. Lockout valves can be actuated by the controller to block the flow of hydraulic fluid to or from both actuators if a maximum allowed tilt angle is exceeded.