PURPOSE: To form crosslinked polymer microparticles by polymerizing an aqueous dispersion of compounds having epoxy groups in the presence of a specified amount of a nitrogen-containing organic compound, followed by isolation.

CONSTITUTION: An epoxy resin obtained by the condensation of an epoxide compound having at least two epoxy groups and an epoxy equivalent of 90 to 300 with an aromatic polyol, in an amount of 20-75 wt.% is mixed under stirring with a condensate of an aliphatic polyol with an epoxide compound, and a dispersant comprising an emulsifier, water and an organic solvent. At most 10 wt.% organic solvent and an appropriate amount of water are added to the mixture to form an aqueous epoxy resin dispersion having a solid content of 10-80 wt.%. This dispersion is heated at 30-100°C under stirring in an inert atmosphere and mixed with a solvent solution of a nitrogen-containing organic compound such as triethylamine in an amount of 0.02-0.15 mol per epoxy equivalent to effect reaction, thus giving crosslinked polymer microparticles of which particles having a mean particle diameter of 0.2-3.0 μm account for 40-70 wt.% and which are based on an epoxy resin having a residual epoxy equivalent of at least 20,000 g/equivalent.