A dispersing agent suitable for suspension polymerization of vinyl compounds, comprising a polyvinyl alcohol resin containing carbonyl groups in its molecule and having a block character of remaining fatty acid ester groups of at least 0.5 and an absorbance of at least 0.1 measured at each of wavelengths of 215 nm, 280 nm and 320 nm with respect to a 0.1% by weight aqueous solution of the polyvinyl alcohol resin, wherein the ratio of absorbance at 320 nm to absorbance at 280 nm is at least 0.3. The dispersing agent has an excellent surface activity and can suppress foaming which may occur in the suspension polymerization of vinyl compounds.