PURPOSE: To provide a production process by which a silicone-vinyl chloride block copolymer having a particle size of 0.1-50μm and a sharp particle size distribution is produced at high polymn. stability in a high yield while producing only a small amt. of aggregates.

CONSTITUTION: A vinyl chloride polymer having a mean particle size of 0.1-50μm is produced by subjecting a vinyl chloride monomer to microsuspension polymn. under such conditions that the monomer is finely dispersed in water contg. an emulsifier in an amt. of 0.8-5wt.% of the monomer and that a polymer having a wt.-average mol.wt. of 2,000-300,000 is used as an oil-sol. polymn. initiator.