Polypropylene(PP)microporous membranes were prepared with the composite diluents of soybean oil and di-n-butyl．phthalate(DBP) via thermally induced phase separation(TIPS)．The effects of nano-CaCO3 nucleating agent and nano—CaCO3／pimelic acid bicomponent nucleating agent on the crystalline morphology and mehing behaviom of the PP／soybean oil／DBP system

and on the microstructure of PP membrane were investigated.The experimental results showed that with addition of 0％～4％ single nano-CaCO3 nucleating agent the peak temperature of melting curve of PP in PP／soybean oil／DBP system varied from 150．7 ℃ to 151．3℃

while the peak melting temperature of pure PP is 165℃．The differential scanning calorimetry(DSC)showed that the addition of bicomponent nucleating agent nano-CaCO3(1％-4％)and pimelic acid(0．5％)induced two peaks on the mehing curve．Wide-angle X-ray diffraction(WAXD)measurements proved that PP formed β—phase and α—phase with addition of bicomponnent nucleating agent nano-CaCO3(1％-4％)and pimelic acid(0．5％)

while the addition of single nano-CaCO3 nucleating agent resulted in only PP crystals of α-phase

which was consistent with the results of DSC．The addition of single nano-CaCO3 nucleating agent in PP／soybean oil／DBP system had unremarkable effect on the morphology of PP membrane．While nano-CaCO3／pimelic acid(1％／0．5％)bicomponent nucleating agent was used

the PP microporous membrane showed smaller and regular pores．When the nano-CaCO3／pimelic acid content was 2％／0．5％and 4％／0．5％。PP micmporous membrane showed more tiny irregular sphendites

as well as larger pores

which were related to the formation of β phase．