Provided is a polyoxyalkylene modified vinyl alcohol-based polymer comprising a polyoxyalkylene group in a side chain, wherein the polymer has a viscosity average degree of polymerization of not less than 150 and not more than 5000, a degree of saponification of not less than 40 mol % and not more than 99.99 mol %, and a polyoxyalkylene group modification rate of not less than 0.05 mol % and not more than 10 mol %; and the polyoxyalkylene group is composed of a polyoxypropylene block and a (poly)oxyethylene block and is represented by the following general formula (I). Such polymer is excellent in temperature-sensitive thickening properties. (in the general formula (I), R1 denotes a hydrogen atom or an alkyl group having a carbon number of from 1 to 8; either one of R2 and R3 is a methyl group and the other is a hydrogen atom; and 10≦m≦40 and 1≦n≦50).