Tannins as compounds of plant biomass seem to be a very useful raw material for an effective bioconversion. This is due to their abundance and renewability as well as the possibility of producing various chemicals and curative preparations from this source. On the other hand, enzymatic removal of tannins from agricultural feedstocks by tannase is very important for production of digestible feed and food products, clarified beverages and fruit juices or instant tea. This article presents a review of information on tannins and their hydrolysis by microbial tannase. Special attention has been paid to chemical structure of tannins and their negative or positive effects on organisms as well as the production of tannase and its biochemical properties. Most promising prospects for the practical applications of tannase in food, pharmaceutical, cosmetic and leather industries are also discussed.