Abstract: Nano-CaCO₃/EPR /PP composite was prepared by the two-roll mill and extruder. The mechanical properties of the composite and the dispersion of EPR and Nano-CaCO₃ were investigated by means of PCM,TEM and mechanical test. The results show that not only the impact property but also the bending modulus of the system have been evidently increased by adding nano-CaCO₃. The toughening mechanism of the nano-CaCO₃ is due to the fact that the addition of nano-CaCO₃ particles makes the EPR well-distributed and the EPR particle size small, leading to the cooperative toughening by the reaction between the smaller EPR particles and the nano-CaCO₃ particles.