Abstract: A detachable computer case comprises a mainboard rack and a detachable board. The mainboard rack has a base, two lateral plates and a rear plate; a plurality of guiding rails formed by pressing and projecting from the upper inner wall of the lateral plates; and a plurality locking stages formed on the top side of the base by pressing and each having a locking hole therein. The detachable board is of inverted-L shape, and has a top plate and a front plate; an indent guiding groove formed by pressing on the outer wall of each lateral side of the top plate; a plurality of locking plates formed on the bottom end of the front plate. The guiding grooves on two lateral sides of the top plate of the detachable board slide backward along the guiding rails on two lateral plates of the mainboard rack, and the locking plates on the bottom end of the front plate of the detachable board are engaged to the corresponding locking holes of the mainboard rack, such that the detachable board is engaged with the mainboard rack.