To provide a dispersion stabilizer for suspension polymerization which is suitable for preparing a vinyl polymer such as a vinyl chloride polymer which has a large volume resistivity, contains few coarse grains and exerts a high plasticizer absorption.

The dispersion stabilizer for suspension polymerization of the vinyl compound comprises a polyvinyl alcohol having an aldehyde group in its side chain which is obtained by saponifying a copolymer of an unsaturated monomer of the formula (wherein R1 and R2 are each hydrogen, a methyl group or a phenyl group; R3 is a 1-8C alkyl group; and n is an integer of 0-8) and a vinyl ester monomer.