A server casing including a casing box and a partition structure is provided. The casing box includes first, second, third and fourth lateral walls connected sequentially and collectively form an accommodating space. The partition structure is detachably disposed in the casing box so as to divide the accommodating space to a plurality of areas. The partition structure includes a main partition and two main fixing sheet sets vertically extending from two opposite edges of the main partition towards opposite directions, and the two main fixing sheet sets are detachably fixed to the first and the third lateral walls of the casing box.