Abstract: Poly(methylmethacrylate/methylacrylate)/organ-montmorillonitc(P(MMn-Mn)/OMMT)nanocompositcs were used to modify poly(vinyl chloride)(PVC)by blending. The compatibility，thermal stability，the dynamical mechanical，tensile and impact properties of the compound were investigated by scanning electron microscope(SEM)，thcrmogravimctric analysis (TGA)，dynamic mechanical thermal analysis(DMA)， tensile and impact test. P(MMA-MA)/OMMT nanocompositcs and PVC exhibited good compatibility，the thermal stability, storage modules，glass transition temperature，and mechanical properties of the composites increased with increasing of nanocompositc content. When the mass ratio of the nanocompositcs and PVC was 20/100，the temperatures of 10%weight loss and glass transition increased by 17. 4℃and 4. 7 ℃ based on neat PVC. The addition of the nanocompositcs also improved the mechanical properties of PVC. The compound showed a set of optimal mechanical properties when the mass ratio of the nanocompositcs and PVC was 30/100，with the tensile and the impact strength being enhanced by 34. 7%and 21.1%，respectively，compared with neat PVC.

Key words: montmorillonitc nanocompositc, polv<, vinvl chloride), blending, modification