The invention provides a method of manufacturing golf balls composed of a core and one or more cover layer which encloses the core, at least one cover layer being a thin layer having a thickness of 1.0 mm or less. The thin layer is formed to a desired thickness on a surface of a core or spherical body by holding within a mold cavity the core or a spherical body composed of the core enclosed by a cover layer and injecting a synthetic resin material into a space defined by a surface of the core or spherical body and an inner face of the mold cavity so as to form a cover layer on the surface of the core or spherical body, then grinding the resulting cover layer to a thickness of at least 0.1 mm with a specific type of grinder. Golf balls obtained in this way can be provided with a good sphericity even when the cover is formed to a very small thickness.