A ball joint includes a tubular boot, an upper end portion and a lower end portion of which are fitted onto an intermediate portion of a shaft of a ball stud and an open end of a housing, respectively. An annular lip portion is formed at the upper end portion of the boot. The lip portion has a first sliding contact face that is in contact with an outer periphery of the shaft, a second sliding contact face that is in contact with a lower face of the knuckle arm, and an annular rib that is formed so as to project inward beyond the first sliding contact face from an upper end portion of the first sliding contact face. The rib is elastically deformed due to contact with the shaft so as to extend along the first sliding contact face and project upward beyond the second sliding contact face.