Abstract: A method for producing an alkali metal hydroxide by electrolysis in an electrolytic cell comprising an anode compartment and a cathode compartment, which comprises supplying an aqueous alkali metal chloride solution to the anode compartment and withdrawing an aqueous alkali metal hydroxide solution from the cathode compartment, wherein a fluorine-containing cation exchange membrane comprising a first layer of an alkali resistant cation exchanger with a thickness of at least 5 .mu.m selected from the group consisting of the following (a), (b), and (c), and a second layer of a perfluorocarbon polymer having --CO.sub.2 M groups (wherein M is an alkali metal) and a water content of from 2 to 7% by weight in a 45 wt% NaOH aqueous solution with a thicknesss of at least 5 .mu.