A playpen includes a top frame, pairs of supporting legs in which the supporting legs of each pair have top ends connected to the top frame at two spaced apart positions and bottom ends extending toward each other, and a fabric enclosure having a lower portion and an upper portion which is attached removably to the top frame. A fixing device includes a plurality of fixing plates adapted to be fixed to the fabric enclosure and each having an engaging hole, and a plurality of foot members each having top and bottom ends, a plate-receiving hole opening at the top end and extending downwardly for insertion of a corresponding fixing plate, two leg-receiving holes for insertion of the bottom ends of one pair of the supporting legs, and a tongue for engaging detachably the engaging hole disposed within the plate-receiving hole.