The invention provides a mold for injection-molding a golf ball, which mold has a cavity inner wall with a vertical diameter connecting both poles in a vertical direction thereof that is longer than a horizontal diameter connecting both poles in a horizontal direction thereof. A method of manufacturing golf balls using such a mold is also provided. The use of this mold eliminates molding problems that arise when molding the outermost cover layer of a golf ball, enabling the cover to be stably molded and also making it possible to easily and reliably obtain golf balls of high symmetry in which a cover of uniform thickness has been formed.