Leather-epoxy interpenetrating polymer networks (IPNs) were synthesized; these IPNs have an approximate epoxy concentration of 25 wt %. The flexural and tensile moduli of the IPNs prepared are equivalent to those of the epoxy resin. The Izod impact energy and fracture toughness measured for the IPNs, however, exceed those attained by the epoxy resin alone by at least a factor of 4. The glass transition of leather-epoxy IPNs occurs over a wide temperature range, thus indicating that the IPN is an intimate admixture of the epoxy resin throughout the collagen matrix of the hide.