Abstract: A double slide way bearing adapted to carry and locate a heavy object such as a machine tool within a plane which includes at least one main body having an upper and a lower rail-receiving grooves formed in its upper and lower surfaces to extend typically in two orthogonal directions. The upper rail-receiving groove is adapted to receive an upper rail bed which fixedly carries the object, while the lower rail-receiving groove is adapted to receive a lower rail bed which is fixed to a base. Between the rail-receiving groove and the rail bed, at each of the upper and the lower sides of the main body, interposed are loaded and unloaded balls which are adapted to roll along respective paths defined by grooves formed in the inner peripheral wall of each rail-receiving groove and in the surface of the associated rail bed, so that the object may be slidingly moved in the directions in which the upper and the lower rail beds extend to any desired position within a plane including the upper rail bed.