A dust cover for a ball joint is made up of a dust cover body made of a rubber elastic material and an annular plate member. In the dust cover body, a reinforcement ring is disposed in a stud mounting part, and an annular step is disposed on the inner peripheral side of the reinforcement ring. The plate member is made up of a plate body and an annular sealing part that is made of a rubber elastic material and is accommodated in the annular step. In the outer periphery of the plate body, a plurality of cut parts are formed, so that outer peripheral petal parts are formed between adjacent cut parts to be capable of being bent so as to be engaged with a knuckle groove.