A lid for mounting on a cup opening defined by a brim of a cup body includes a cover having a substantially planar portion and a recessed opening disposed on the cover; a side wall disposed around the periphery of the cover; a flange extended from the bottom edge of the side wall and forms a trench space for accommodating the brim of the cup body when the lid is mounted on the cup opening; and a breathable film disposed below the substantially planar portion and covered the recessed opening of the cover. The cover and the breathable film of the present lid are integrally formed into a single piece.