Lactobionic acid is produced by the oxidation of lactose and has been reported to promote calcium absorption in the intestine. Lactobionic acid also promotes the intestinal production of equol, which has been reported to prevent menopause. Thus, an efficient and safe production method of lactobionic acid was required for its application to food products. Although a wide variety of lactose oxidation methods have been reported, no suitable production method had been developed for lactobionic acid. We found lactobionic acid in a Caspian Sea yogurt and estimated the annual intake of lactobionic acid based on daily yogurt consumption. The lactobionic acid-producing bacterium was identified as an acetic acid bacterium. This bacterium is one of the main fermentation bacteria in this yogurt. In collaboration with a company, we developed a method for the commercial production of lactobionic acid using an acetic acid bacterium. Consequently, a number of food products containing lactobionic acid are now commercially available on the Japanese market. Acetic acid bacteria were previously reported to be unable to oxidize lactose because their sugar-oxidizing enzyme—a membrane-bound glucose dehydrogenase−does not show lactose-oxidizing activity. In contrast, we demonstrated that the glucose dehydrogenase of the acetic acid bacterium could oxidize lactose.