Abstract: An anti-theft device for locking an outboard motor comprising an elongated, channel-like, body member has a longitudinally extending opening to closely receive the head portions of clamping screws which clamp the motor to a transom board of a boat, or a motor stand for use in motor sales and/or service. The body member includes a slot to receive the shanks of the screws while allowing the screws to pass through the body member while the head portions are confined within the body member. Stops within the longitudinal opening in the body member are shaped to fit within recesses or notches in the head portions of the clamping screws. Locking means including a padlock secure the head portions of the clamping screws tightly within the body member and in contact with the stops to prevent rotation of the clamping screws.