A mounting mechanism for a server or other electronic apparatus allowing the addition of modules or devices of different sizes includes a casing having an opening. A guiding track is disposed in the casing; a slide bar is movably disposed on the guiding track; a restriction structure is disposed on the first end of the guiding track; and a locking structure can pivot on the restriction structure. When the casing is mounted on a rear rack, the slide bar is moved out of the casing via the opening, and the restriction structure and the locking structure are securely fastened to the frame.