Polymeric hollow microspheres of a few ten mu m in diameter were prepared by removal of the encapsulated solution from polymeric microcapsules by in situ polymerization. As a result, no rupture of microcapsules occurred and a high yield of polymeric hollow microspheres was obtained under the condition of lower ratio of the encapsulated solution to monomer and slower rate of solution removal. The compressive stress to rupture of hollow microspheres increased with decreasing encapsulated-solution/ monomer ratio and removal rate of encapsulated solution.