An object of the present invention is to provide a dispersion assistant that, when used for suspension polymerization of a vinyl-based compound, achieves stable production of a good polymer (vinyl-based resin) without much scale adhesion on the polymerization tank even in the cases where used in a large amount. Provided is a dispersion assistant for suspension polymerization, which comprises a polyvinyl alcohol-based polymer (A) having an acetal group (a) having an olefinic unsaturated double bond, the polymer having a saponification degree of 60 mol% or less.