Modified vinyl alcohol polymer powder having reduced methanol content and production method therefor, and water-soluble film and packaging material

The present invention provides: an environmentally-friendly, industrially-useful modified vinyl alcohol polymer powder containing a structural unit derived from a derivative of an ethylenically unsaturated dicarboxylic acid, wherein the contained amount of methanol present in the powder is reduced, and the amount of insoluble components is small when the powder is dissolved in water; and a method for producing the polymer powder. The present invention pertains to a modified vinyl alcohol polymer powder containing a structural unit derived from a derivative (A) of an ethylenically unsaturated dicarboxylic acid, the contained amount (X) of the structural unit being 0.05-10 mol%, and having a saponification degree of 80.0-99.9 mol%, wherein the methanol content of the polymer powder is not less than 0.01 wt% but less than 3.0 wt% when 500 mg of the polymer powder is measured using a headspace gas chromatography, and the amount of components insoluble in an aqueous solution thereof with a concentration of 5 wt% at 90°C is not less than 0.1 ppm but less than 2000 ppm.