A simple and convenient method for measuring kLa in large-scale fermentors was proposed. This method was based on the measurement of the dissolved oxygen concentration under steady state conditions established by an equivalency of the sulfite ion feed and chemical oxidation rates. This method had the following advantages: It was a steady state method, and so it was not necessary to consider the response lag of a dissolved oxygen probe and the response lag due to gas phase mixing in fermentors. The oxygen content of the effluent gas in this measuring system was nearly the same as that of the sparged air. Therefore, it was possible to use the oxygen partial pressure of the sparged air for the calculation of the driving force of oxygen transfer. The detailed information on the kinetics of sulfite oxidation was not necessary, because the dissolved oxygen concentration in steady state was not influenced by sulfite oxidation rates. The kLa measurement was finished in as short a period as 150 s, even in a fermentor with a volume of 10 m3. Since the amount of Na2S04 accumulation in the test fermentors was very small because of the quick measurement, the kLa values obtained by this method were applicable to the electrolyte-free system. Furthermore, we could discharge the used liquid from the fermentors into a drain without any pretreatment due to the low salt concentration.