A production process for heat-expanded microspheres includes the step of providing a gaseous fluid containing heat-expandable microspheres, which includes a shell of thermoplastic resin and a blowing agent encapsulated therein having a boiling point not higher than the softening point of the thermoplastic resin and have an average particle size from 1 to 100 μm. The gaseous fluid is fed through a gas-introducing tube having a dispersion nozzle on its outlet that is fixed inside a conduit having a hot gas flow flowing therethrough. A jet of the gaseous fluid is emitted through the dispersion nozzle. Further, the gaseous fluid is collided on a collision plate fixed under the dispersion nozzle so as to disperse the heat-expandable microspheres in the hot gas flow. The dispersed heat-expandable microspheres are heated in the hot gas flow at a temperature not lower than their expansion initiating temperature and thus expanded.