n-Propanol was converted to propionic acid by Gluconobacter oxydans CCM 1783 (ATCC 621). Gluconobacter oxydans cannot grow on propanol as a sole carbon source, but is able to convert it to propionic acid. Glycerol was used as an assimilatable cosubstrate. For the purposes of optimizing the conditions for conversion, various influences were examined by oxygen consumption evaluation : the influence of propanol on growth, the effect of pH on the propanol and propionaldehyde conversion rate, and inhibition by propanol and by propionate. On the basis of these results the following procedure was proposed for conversion : fed-batch conversion at pH 6.0, propanol feeding delay after the growth phase, and propanol feeding controlled by actual oxygen concentration. In the fed-batch conversion, final concentrations of 37 g of calcium propionate per liter within 30 h and 56 g of sodium propionate per liter within 70 h were obtained. The yields obtained were near the theoretical values.