To obtain a microcapsulated copolymer of both a hydrophilic monomer and a hydrophobic monomer having a particle size as uniform as possible by adding the hydrophilic monomer to an aqueous phase.

(A) A microcapsulated hydrophobic monomer dispersed in an aqueous phase is polymerized by adding (B) a hydrophilic monomer to the aqueous phase. A monoethylenically unsaturated compound having <2 wt.% solubility in water at 25°C is used as the component A. To be concrete, styrene, vinyltoluene, ethylstyrene, α-methylstyrene, or the like, are used as the component A. A monoethylenically unsaturated compound having at least 2 wt.% solubility in water at 25°C is used as the component B. To be concrete, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, or the like, is preferably used as the component B.