Abstract: A service vehicle ladder lock for fastening a step or extension ladder to a conventional ladder rack running either along a side of the roof of the vehicle or across the top thereof. This ladder lock forms a rectangular framework for placement about the ladder and the ladder rack in close proximity to inhibit movement in any direction upon rapid starting or stopping. In the preferred configuration the ladder lock comprises three portions of narrow bent flat metal stock fastened together wherein the first and second portions are attached by a hinge to allow opening and closing; and the second and third portions are attached to each other. The free end of the first portion has a strike plate thereon for receiving the latch of a tension latch/lock assembly integrally mated to the free end of the third portion. This ladder lock optionally includes means for adjusting the frame width and/or height to insure a close fit around the ladder and the ladder frame to insure safety and security thereof.