The present invention aims to provide a method for producing a modified molded article that has favorable appearance, high breaking strength, and excellent abrasion resistance, as well as excellently low permeability to nitrogen gas and hydrochloric acid. The method for producing a modified molded article of the present invention includes molding a fluororesin to provide a molded article and irradiating the molded article with radiation at an irradiation dose of lower than 100 kGy at 50° C. to 200° C. to provide a modified molded article.