Abstract: A plastic buckle consisting of a one-piece plastic molding has a belt insertion hole defined by top and bottom walls facing each other and opposite side walls facing each other. The front wall of the buckle has a lock portion defined by a U-shaped slit-like opening. The lock portion is elastically deformable and has a lock pawl provided on the inner side of its end portion. The opposite side walls are provided with side holes communicating with the belt insertion hole. Operating members penetrate the side holes to be inwardly elastically deformed to be brought into contact with the side portions of the lock portion to cause an upward displacement of the free end of the lock portion.