Abstract: A process for production of a vinyl polymer by suspension polymerization or emulsion polymerization of at least one kind of vinyl monomer in an aqueous medium is disclosed.In this process, the polymerization is carried out in a polymerizer, the inner wall surface and portions of the auxiliary equipment thereof which may come into contact with the monomer during polymerization having a surface roughness of not greater than 5 .mu.m and being previously coated with a scaling preventive comprising at least one selected from dyes, pigments and aromatic or heterocyclic compounds having at least 5 conjugated .pi. bonds. According to this process, scaling on the inner wall surface of a polymerizer, etc. during polymerization can be prevented effectively and surely.