Abstract: A swivel assembly of a vehicle seat including a ring-shaped upper plate fixed to a seat side member of a vehicle; a ring-shaped lower plate fixed to a floor side member of the vehicle; and a set plate holding the upper plate between it and the lower plate. One ball is provided between the upper plate and the lower plate. The other ball is provided between the upper plate and the set plate. The other ball is in contact with both inner surfaces of each of one sectionally V-shaped guide groove and the other sectionally V-shaped guide groove confronting the one groove. The upper plate can be held at a predetermined position without being loosened vertically and horizontally even though the upper plate, the lower plate, and the set plate have errors occurred in manufacture.