Abstract: Waste vulcanizate powder (RP) was used as an active filler to modify bulk molding compounds (BMC) based on unsaturated polyester. Effects of various factors such as formulation, preparation technologies on toughening results were systematically studied, and a preliminary discussion on toughening mechanism of RP was also made. Results show that the toughening effectiveness is related to the process of pretreatment, amount of stuff, particle size and type of RP used. When monomer/RP1=50/50, particle size=0.28 mm, and amount of stuff=20 phr, impact strength of BMC increases from 5.2 without RP to 11.4 kJ/m², molding shrinkage decreases from 0.5% to 0.1%, whereas other mechanical properties basically remain unchanged. Analyses of TEM and electronic probe prove the formation of a gradient interpenetrating polymer network (IPN) in the vicinity of phase boundaries between RP and the matrix of BMC. The IPN strengthens combination of interfaces of the two phases, enhancing the impact strength of BMC.