Abstract: A continuous process for the production of chlorine dioxide by the electrolysis of an aqueous solution of sodium chlorite is provided. The process comprises electrolyzing the aqueous sodium chlorite solution to produce chlorine dioxide which dissolves to produce an aqueous solution of NaClO.sub.2 containing chlorine dioxide. The aqueous solution of sodium chlorite-containing ClO.sub.2 is passed through a photometric cell to measure the chlorite ion concentration as a function of the color produced by the ClO.sub.2 -NaClO.sub.2 -H.sub.2 O system. Chlorine dioxide gas is removed from the aqueous solution and recovered.The novel process of the present invention employs solutions containing low, accurately controlled concentrations of sodium chlorite ion which when electrolyzed avoid the formation of by-products such as a dark colored chlorine dioxide complex and sodium chlorate.