A method for manufacturing an implantable film and a prosthesis comprising such a film The present invention relates to a method for manufacturing a non porous film intended to be implanted in the human body, said method comprising the following steps: preparation of a first film, called intermediate film, via gelling of a starting solution comprising at least one polymer selected in the group consisting of collagen, glycosaminoglycans, and mixtures thereof, immersion of said intermediate film in an alkaline composition comprising at least one C1-C4 alcohol, drying of the film obtained at the end of the immersing step. The invention also relates to a method for manufacturing a prosthesis comprising a textile support and such a film.