A mounting apparatus for mounting an optical sight on a rifle has an elongated rail and a mounting base projecting downwardly from the rail for securing the rail on a rifle. The rail has an upwardly facing channel extending along its length for receiving a mounting element of a first type of optical sight, the base of the channel having a plurality of openings for receiving fastener devices for selectively securing an optical sight at a selected location along the length of the rail. The opposite sides of the rail each have a plurality of spaced tabs forming a Picatinney rail for mounting a second type of optical sight having a mounting element for engaging over the Picatinney rail. The mounting rail therefore combines the mounting formations for two different types of optical sight in a single rail.