Provided is a modified polyvinyl alcohol containing 0.1 to 10 mol % of a monomer unit represented by formula (1) below and having a degree of polymerization exceeding 2000. This provides a modified polyvinyl alcohol an aqueous solution of which foams less and which has excellent film strength and gas barrier properties under high humidity conditions, while having excellent water solubility. [In formula (1), R1 represents a hydrogen atom or a methyl group.]