The invention relates to a process for producing 2-keto-L-gulonic acid, which comprises converting L-sorbose and/or D-sorbitol into 2-keto-L-gulonic acid with the aid of a microorganism or its cell free extract, said microorganism belonging to the species Gluconobacter oxydans capable of producing 2-keto-L-gulonic acid and having a high activity of L-sorbose dehydrogenase to convert L-sorbose into L-sorbosone. Specific microorganisms useful in such process are also part of the invention.