A ball joint provided with a ball stud having a ball section at one end thereof, a socket for housing the ball section, and an elastically deformable anti-friction seat mounted between the ball section and the socket and rotatably supporting the ball section, wherein the socket and the anti-friction seat have an opening through which the stud section of the ball stud can be inserted in a loose fit condition. Bases and grooves are arranged in the inner surface of the anti-friction seat so as to extend in a direction across the peripheral edge of the opening and be alternately arranged in the circumferential direction extending along the peripheral edge of the opening. Each of the grooves is isolated from the opening by a partition wall extending between bases on opposite sides of the groove. The bases are in spherical contact with the ball section, and the grooves are filled with a lubricating agent.