A sealing ring is an elastic annular member with an engaging groove for insertion of an insertion member. The engaging groove includes a sealing surface and an opposite abutting surface which is inclined from the bottom of the engaging groove toward the open end of the engaging groove, so that the open end of the engaging groove is narrower than the bottom of the engaging groove. When the insertion member is inserted in the engaging groove, the abutting surface and the sealing surface will transmit pressure to make the abutting surface of the abutting portion and the sealing surface of the sealing lip of the sealing ring are pressed against two sides of the inserted insertion member. Therefore, the sealing performance of the sealing ring is improved.