A soy-based resin was prepared by the process of transesterfication and epoxidation of regular food-grade soybean oil. The soy-based resin was used as a reactive diluent and also as a replacement of bisA epoxy resin in an anhydride-cured polymer. The curing efficiency of soy epoxy resin was studied using differential scanning calorimetry. Physicochemical properties and fracture behavior of soy-based resin polymers were studied using dynamic mechanical analysis and fracture toughness measurements, respectively. Toughness measurements were carried out using the compact tension geometry following the principles of linear elastic fracture mechanics. Tests showed that the addition of soy-based epoxy resin to the base epon resin improved the toughness of the blend. Morphology of the fractured specimens has been analyzed by scanning electron microscopy. The soy-based resins hold great potential for environmentally friendly, renewable resource based, and low cost materials for structural applications. (c) 2007 Wiley Periodicals, Inc.