Abstract: An anti-theft device for clamping and locking an outboard motor to a transom board comprises a bracket forming together with an upper part of the outboard motor a substantially U-shaped suspension rack for mounting the outboard motor on the outboard transom side, and a free leg of the bracket extending downwardly along the inboard transom side. also included is a clamping fixture in the form of a jack screw including a hollow body and a clamping screw for urging the free leg away from the inboard side, while clamping the motor to the outboard side. The hollow body forms a protective housing having openings in its walls for receiving and shielding the screw shank, and supports at one end an open ended casing for receiving and shielding the screw head and a key-operated lock for locking the screw against rotation; the said housing and the casing are separated by a partition having an opening, and the screw shank extends from the casing into the housing through such opening.