The invention provides a method of manufacturing golf balls having a core and at least one cover layer which involves injecting a molten cover resin material around a core so as to form a cover layer. The cover resin material is a single resin composition made up of (A) a thermoplastic polyurethane, (B) a polyisocyanate compound and (C) a thermoplastic elastomer other than the thermoplastic polyurethane in a weight ratio (A):(B):(C)=100:{2-50}:{0-50}, and is injected with from 10 to 99% of the total number of isocyanate groups in component B remaining in an unreacted state within the cover resin material. The method of the invention provides a high manufacturability and a good amenability to mass production, and the manufactured golf balls thus obtained have a high rebound and excellent scuff resistance.