A modified PVA that enables formation of a film superior in cold water solubility, mechanical strength, and chemical resistance is provided. The modified PVA comprises a monomer unit represented by formula (I), and a structural unit represented by formula (II): wherein: a content of the monomer unit (I) is from 0.05 mol% to 10 mol%, and a content of the structural unit (II) is from 0.001 mol% to 0.5 mol% with respect to the total monomer units in the modified PVA; a viscosity average degree of polymerization is from 300 to 3,000; and a degree of saponification is from 82 mol% to 99.5 mol%. In the formula (I): R 1 represents a hydrogen atom, or a methyl group; and R 2 represents -R 3 -SO 3 -X + , -R 3 -N + (R 4 ) 3 Cl - , or a hydrogen atom, R 3 representing an alkanediyl group, X + representing a hydrogen atom, a metal atom, or an ammonium group, and R 4 representing an alkyl group.