In manufacturing a barrier-forming film, a vapor-deposited inorganic oxide film is provided on a face of a substrate film. An annealing treatment is applied to the substrate film having said vapor-deposited inorganic film. The substrate film is a resinous film which selected from a group consisting of polyesters, polyamides and polypropylenes. The annealing treatment includes a heating treatment carried out at a temperature within the range from 55.degree. C. to 150.degree. C. in order to cause thermal shrinkage of the substrate film and to increase density of the vapor-deposited inorganic oxide film. The vapor-deposited inorganic oxide film includes a vapor-deposited silicon oxide film or a vapor-deposited aluminum oxide film.