PURPOSE: To obtain a dispersant which is used for the suspension polymn. of an ethylenically unsatd. monomer and can give an easily processible high-quality polymer by using a polyvinyl alcohol having a specific structure.

CONSTITUTION: This dispersant for the suspension polymn. of an ethylenically unsatd. monomer is a polyvinyl alcohol polymer which has a structure represented by the formula in the molecule, gives a 1wt.% aq. soln, having an absorbance at 280nm of 2.5 or higher, and has an average degree of polymn. of 500 or higher, a degree of saponification of 60-90mol.%. a ratio (Mw/Mn) of wt. average mol.wt. (Mw) to number average mol.wt. (Mn) of 2.5 or lower, a block character to degree of saponification of 0.45 or lower, and a methanol- sol. content of 10wt.% or lower. The dispersant is esp. suitable for polymerizing vinyl chloride or a monomer mixture contg. vinyl chloride.