A dust cover for a ball joint has a spherical head portion, a shaft, a cylindrical one-end large-diameter opening portion, a large-diameter opening portion side reinforcing ring fixed to a socket, the other end small-diameter opening portion retained onto the shaft, a flange portion extending from an end portion in the other-end small-diameter opening portion of the one-end large-diameter opening portion toward a ball stud side, and a rubber-like elastic film portion coupling an inward end portion of the flange portion and the other-end small-diameter opening portion. The dust cover has an outside projection provided on an outer peripheral surface of the film portion, and an inside projection provided on an inner peripheral surface of a joint portion between the flange portion and the film portion, and the outside projection and the inside projection come into contact with each other when the dust covers for the ball joint are laminated.