A liquid ejection head has a plurality of ejection ports for ejecting a liquid, and a housing provided with a pair of liquid chambers which supply the liquid to a corresponding ejection port. A method for manufacturing the liquid ejection head includes: arranging a pair of mold pieces, of which width decreases gradually, to adjoin in the width direction thereof with the width decreasing in the opposite directions, molding a housing, and forming the pair of liquid chambers by drawing the pair of mold pieces from the molded housing in the direction in which the width increases.