A resin composition comprises a thermoplastic resin, a non-terpene-series higher fatty acid or a derivative thereof and a black pigment. As the higher fatty acid or derivative thereof, use can be made of, for example, a saturated higher fatty acid having about 12 to 30 carbon atoms or a metal salt thereof. As the thermoplastic resin, use can be made of, for example, an acrylic resin A and a styrenic resin B. As the black dye or pigment, use can be made of, for example, carbon black. The resin composition may contain a dye or pigment such as titanium oxide. A clearly defined white marking is developed on the above resin composition by laser irradiation.