To obtain an N-vinylamide/vinyl acetate copolymer hydrolyzate in a powder form at a low cost by hydrolyzing a copolymer formed from an N-vinylamide and vinyl acetate and washing the resultant product with at least one agent selected from among water, an alcohol and salt water at a specified temperature or lower.
The copolymer is suspended in water, then hydrolyzed under basic conditions and washed at 20°C or lower. Usually, a copolymer comprising 1-50 mol% N-vinylamide units and 50-99 mol% vinyl acetate units is used. N- vinylformamide is favorable as a monomer for forming the N-vinylamide units. The concentration of the polymer in hydrolysis is usually 1-50 wt.%. The hydrolysis is done preferably in the presence of a strong alkali. After the completion of hydrolysis, the liquid changes into a slurry. The slurry is subjected to solid- liquid separation, then washed and dried to give a powder.