Heat-expandable microspheres having high heat resistance and high solvent resistance, a production process thereof include a shell of a thermoplastic resin and a thermally vaporizable blowing agent being encapsulated therein. The thermoplastic resin includes a copolymer produced by polymerizing a polymerizable component containing a carboxyl-group-containing monomer. The surface of the heat-expandable microspheres is treated with an organic compound containing a metal of the Groups from 3 to 12 in the Periodic Table.
