An original chlorate cell system equipped with an oxygen cathode, a DSA(R) and a separate reactor was set up. A method for determining the current efficiency by means of measuring the flow capacity of cell gas in the chlorate cell process has been proposed. This method is simple and convenient as well as accurate in evaluation of the chlorate current efficiency in the chlorate cell with an oxygen cathode, compared to the traditional method of analysis. The current efficiency of the anode can be estimated with the gas analysis method.