It is possible to perform microencapsulation of a bioactive substance having a solid form at ordinary temperature in a predetermined wall thickness and particle size without the need of dissolving the solid biologically active substance in any solvent by a method for producing a microcapsule, comprising: heating an aqueous dispersion comprising a dispersion stabilizer, an ionic surfactant, the solid biologically active substance, a polymerization initiator and a radical-polymerizable monomer subjected to ultrasonic irradiation. Therefore, the method enables to design a desired particle readily and it is useful for the microencapsulation.
