A differentiation between free carboxyl and various lactone groups in oxycelluloses was carried out based on the variation in their reaction rates with KI–KIO3 solution. An attempt has been made to identify the various lactone groups present by comparison of the results of different oxycelluloses as well as study on some model compounds. A characteristic and group spectrum was determined for each oxycellulose. On blocking the free carboxyl groups by zinc acetate treatment, the results for the nature and amounts of various lactones present are in good agreement with the results for oxycelluloses themselves. Sodium borohydride treatment for 120 hr has been found to be incapable of reducing all the lactones present. An appreciable decrease in the value for glucono-δ-lactone was observed, whiles glucuronic acid lactone was only partially attacked. Treatment with chlorous acid resulted in an increase in the values for free carboxyl as well as lactones for all oxycelluloses.