Phenolic novolac resins have been modified with chestnut tannin for reduction of phenol content in resins. In this work, rheological and kinetic analysis of curing reactions of these resins with hexamethylenetetramine (hexamine) has been performed. Chemical structure of obtained materials has been analyzed and compared with that of nonmodified resins. Results reveal that cure reactions of resin modified with chestnut tannin are different when compared with nonmodified novolacs not only in the cure kinetics values but also in final chemical structure. (c) 2006 Wiley Periodicals, Inc.