Abstract: In electrolytic cell for use in electrolysis of aqueous alkali metal chloride solutions, which comprises one or more vertical expandable anodes, one or more vertical cathodes and one or more cation-exchange membranes each located between a pair of the opposite anode and cathode plates; an improvement is now provided, which is lying in the newly devised cathode structure comprising a vertical cathode, a flexible and foraminate metal mesh of low hydrogen-overvoltage removably mounted on one side of said cathode, a hydraulically permeable and hydrogen gas bubbles-impenetrable microporous film removably mounted on said metal mesh, and a cation-exchange membrane removably mounted on said microporous film, in such way that the expandable anode as located adjacent to said cation-exchange membrane is able to exert a resilient force to push the cation-exchange membrane against the microporous film, the metal mesh and the cathode plate; and to bring the latter elements into close contact with each other.