An exemplary electronic device enclosure includes a box, a mainboard having a plurality of slots, a card having a bottom end fixed in one slot of the mainboard, and an opposite top end, and a locking device. The locking device includes a fixing member and an engaging member. The fixing member includes a plurality of first teeth. The engaging member includes a plurality of second teeth matching with the first teeth, a bottom of the engaging member having a cutout defined therein, and the cutout adapted for receiving an edge of the card. The engaging member is operable so that the second teeth engage with various of the first teeth, whereby a location of the engaging member is adjustable relative to the location of the fixing member, and thereby the engaging member is capable of engaging with the card when the card is at different locations.