A masterbatch containing an organic base component and heat-expandable microspheres including a thermoplastic resin shell and a thermally vaporizable blowing agent encapsulated therein. The organic base component has a melting point not higher than the expansion-initiation temperature of the heat-expandable microspheres and a melt flow rate (MFR, g/10 mm) higher than 50 and not higher than 2200. A ratio of the heat-expandable microspheres ranges from 30 to 80 wt % of the total weight of the heat-expandable microspheres and the organic base component. Also disclosed is a molding composition, a foamed molded article manufactured by molding the molding composition and a weathers tripping.