A server casing includes a shell, a top cover, two first slide rails and two second slide rails. The shell includes two side frames. The two side frames are connected to the two sides of the shell. The top cover is movably disposed on the shell and includes an upper part. The two side parts are connected to the two sides of the upper part. Each first slide rail includes a first body part and a first extension part. The two first body parts are fixed to the two side frames of the shell. Each second slide rail includes a second body part and a second extension part. The two second body parts are fixed to the two side parts of the top cover. Each first extension part of each first slide rail are corresponding to and assembled with each second extension parts of each second slide rail.