A polymer film comprises a polymer composition containing (A) a cyclic olefin polymer containing an olefin unit having a C3-10alkyl group as a side chain thereof and (B) a chlorine-containing polymer. The chlorine-containing polymer (B) may comprise a vinylidene chloride-series polymer. The ratio of the chlorine-containing polymer (B) relative to 100 parts by weight of the cyclic olefin polymer (A) may be 0.5 to 60 parts by weight. The film has a moderate releasability from an electrolyte membrane and an electrode membrane of a polymer electrolyte fuel cell and a moderate adhesion to the electrolyte membrane and the electrode membrane and can adhere to a commonly-used substrate film without interposition of an adhesive layer such as an easily adhesive layer. The film is thus suitable as a release film for producing a membrane electrode assembly of a polymer electrolyte fuel cell.