A castor includes a castor body, a first bushing mounted on a top of the castor body, a bearing mounted in the first bushing, a top cover mounted on the top of the castor body to cover the first bushing and the bearing, a second bushing mounted on a bottom of the castor body, and an upright shaft in turn extending through the top cover, the bearing, the castor body and the second bushing. Thus, the distance between the top cover and the second bushing is increased so that the bearing and the castor body can bear a heavier load. In addition, the distance between the top cover and the second bushing is increased so that the upright shaft and the second bushing can bear a greater rotational force.