A bearing lubrication system for an extension housing of automatic transmission, including an extension housing connected to a transmission case, a valve casing of a hydraulic control system fastened to the transmission case, a transmission output shaft supported in the extension housing, and a sleeve yoke splined to the output shaft and fitted in a bearing portion of the extension housing through a bearing, characterized in that the lubrication system is provided with a forced lubrication means comprising: a bearing lubricant tapping passage branched off from a lubricant oil passage or line pressure conduit in the transmission case or in the valve casing; a bearing lubricant supply passage communicating the bearing lubricant tapping passage with the bearing portion of the extension housing; and a flow control throttle provided in the bearing lubricant tapping passage or in the bearing lubricant supply passage.