Abstract: An anti-theft device is provided for use with semi-trailers of the type which have a Dolly-Leg, a Dolly-Leg crank, and a Dolly-Leg crank handle. The anti-theft device includes a housing, a locking bar, and a lock. The housing has a top, an end panel, a first side, a second side, and a notched bottom, with the first side and the second side each having formed therein a first side aperture and a second side aperture respectively. The notched bottom has downwardly depending therefrom at least two lock chain guide harnesses. The locking bar has formed therein at one end thereof a locking bar aperture. The locking bar extends through both the first side and the second side of the housing, such that the locking bar passes through both the first side aperture as well as the second side aperture. The lock is secured to the locking bar by attachment thereto through the locking bar aperture. The device also preferably includes a chain, with the chain also being secured to the locking bar.