Abstract: A mechanical anti-theft device for motor vehicles which includes, essentially, gripper means capable of engaging the cross section of a tire and a wheel rim of a wheel of the motor vehicle so that it closes on a pivot around the tire and the wheel rim; a support bar for the gripper means; an actuator rod, connected to the gripper means, which slides with relation to the bar in such a way that it can be moved, manually, between a first, unlocked, position, when it controls the opening of the gripper means and a second, locked, position, when it controls the closure of the gripper means around the tire and wheel rim; elastic means are also envisaged, placed between the bar and the rod, capable of holding the rod in the unlocked position, and also items, associated with the rod and capable of engaging with the bar in order to lock the rod with respect to the bar in the closed position.