A sliding window track cover that is adjustable to fit different window track widths and also acts as a window locking mechanism. The window track cover is comprised of a male and female subassembly fastened together. The female subassembly has a pair of spaced, parallel, longitudinally extending flange plate members, a longitudinally extending leg member attached to said flange plates along one longitudinal edge thereof, and a longitudinally extending shoulder member. The male subassembly has a longitudinally extending tongue plate, a longitudinally extending leg member attached to the tongue plate adjacent one longitudinal edge thereof, but inboard a distance sufficient to form a shoulder. The tongue plate of the male subassembly is inserted into the slot formed between the flange plates of the female subassembly a distance sufficient to cause the male and female leg members to be spaced apart a distance that is substantially the same as the distance between the side walls of a window track. Mating corrugations in one of the flange plate members and in the tongue plate member lock the two subassemblies into the selected configuration.