Electrolytic process using novel diaphragm

In an electrolysis process for brine wherein a diaphragm is utilized in an electrolytic cell, the improvement wherein said diphragm is of a size of at least 1 cm in length in at least two directions, said diaphragm having permeability to water of 0.003 - 0.32 ml/cm.sup.2 /hr/cm.H.sub.2 O and comprising a diaphragm base composed of inorganic fibers selected from the group consisting of asbestos and graphite fibers and a fluorine-containing resin, said fluorine-containing resin being present in an amount of 0.5 - 60% by weight based on the weight of said diaphragm, and said diaphragm being prepared by homogeneously blending a dispersion of said inorganic fibers with said fluorine-containing resin, forming said blend into a film, and then heat treating said film so that said resin is locally sintered and adhered to the film.