A play yard can be locked in an unfolded position via a latch mechanism or unlocked by the latch mechanism to fold to a folded position, by means of lifting a central member and bringing the rail members, the upper support members, the lower support members, and the connecting members to rotate toward the center of the play yard. A spring-loaded engaging member disposed on the rail member can have engagement with the bracket so that the play yard can be stably retained in the folded position. When the engaging member is operated to disengage from the bracket, the rail members, the upper support members, the lower support members, and the connecting members rotate away from the center of the play yard all the way to the unfolded position until the connecting members can be locked by the latch mechanism, which retains the play yard in the unfolded position.