PURPOSE: A water-resistant polymer suitable as a base for polarizing films or the like, obtained by copolymerizing polyvinyl alcohol with a carboxyl group- containing polymer-izable vinyl monomer and a polymerizable vinyl monomer reactive with the carboxyl group.

CONSTITUTION: A carboxyl group-containing polymerizable vinyl monomer (e.g., acrylic or maleic acid) and a polymerizable vinyl monomer which can react with a carboxyl group to form a chemical bond (e.g., N-methylolacrylamide or 2- hydroxyethyl acrylate) are added to an aqueous dispersion or solution of polyvinyl alcohol. A polymerization initiator (e.g., cerium ammonium sulfate) is added thereto and the mixture is polymerized to obtain the purpose water-resistant polymer. A water-resistant polarizing film film of excellent polarization characteristics can be obtained by, for example, a method comprising forming the above polymer into a film and orientating this film after impregnation with a dichroic dye or/and iodine.