Abstract: A process for tapering synthetic fibers at the end portion thereof comprising the steps of inserting synthetic fibers into a supersonic vibration-given etching liquid to an extent that only the end portion of the fibers is immersed therein, withdrawing the fibers from the supersonic vibration-given etching liquid and then washing the treated fibers in a supersonic vibration-given washing liquid, the insertion and withdrawal being alternately repeated each at a predetermined velocity. In one embodiment, the etching liquid has abrasive particles suspended therein or an abrasive brush provided therein.