Modified polyvinyl alcohol contains a monomer unit having a carboxyl group, wherein the modified polyvinyl alcohol has a degree of saponification of from 50 to 99.99 mol % and a viscosity-average degree of polymerization of from 200 to 5000 and satisfies formulae (1) to (3) below. The modified polyvinyl alcohol of the present invention thus obtained is particularly excellent in dispersibility in water. 0.8≦(MwUV/MwRI)≦1.2  (1) 2≦(MwUV/MnUV)≦8  (2) 0.01≦A280≦0.8  (3)