Abstract : In this preliminary study, two novel hyperbranched polymer (HBP)/epoxy blends were evaluated to determine their efficiency as blend modifiers and tougheners in a brittle epoxy resin. The HBP is miscible in the epoxy and phase separates as cure progresses to form a two-phase system with a dispersed secondary phase of HBP/epoxy compatibilizers in a rigid epoxy matrix. There is no significant increase in the viscosity of the blends when compared to the pure epoxy. This demonstrates an improved processibility over conventional tougheners. A modest increase in the fracture toughness was achieved in both systems but at different concentrations of HBP Further improvements in the toughness may be realized in an epoxy system when these novel molecules are used in concert with chain expanders.