Heat-expandable microspheres including a thermoplastic resin shell and a thermally-vaporizable blowing agent encapsulated therein. The thermoplastic resin is produced by polymerizing a polymerizable component containing (A) a nitrile monomer including acrylonitrile and methacrylonitrile, (B) a carboxyl-group-containing monomer, and (C) a monomer copolymerizable with the nitrile monomer (A) and the carboxyl-group-containing monomer (B). Further, the amount of the acrylonitrile in the nitrile monomer (A) ranges from 0.1 to 9 wt % based on the nitrile monomer (A). Also disclosed are hollow particles manufactured by heating and expanding the heat-expandable microspheres; a composition containing a base compound and at least one particulate material selected from the heat-expandable microspheres and the hollow particles; and a formed product manufactured by molding or applying a coat of the composition.