A production process for heat-expanded microspheres comprising the step of providing a gaseous fluid containing heat-expandable microspheres, which comprise 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, feeding the gaseous fluid through a gas-introducing tube having a dispersion nozzle on its outlet and being fixed inside a hot gas flow, and emitting a jet of the gaseous fluid through the dispersion nozzle; a step wherein 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; and a step wherein 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. The production process results in minimum difference in the variation coefficient of particle size distribution between the microspheres before and after heat-expansion, slight ratio of raw microspheres and slightly expanded microspheres contained in resultant heat-expanded microspheres, and suppressed formation of aggregated microspheres.