Abstract: Nano-CaCO3 modified polypropylene composites were prepared using supercutical fluid technology, and the effects of nano-CaCO3 on foamed effect and mechanical properties of the composite, and on the rheological property of blend including CaCO3 and polypropylene were studied. The results show that the foamed effect of the composite was first good and then poor, and the tensile strength and impact toughness all increased and then decreased with the increase of nano-CaCO3 addition. When the addition of nano-CaCO3 was 5wt%, the composite had the best foamed effect and mechanical properties, the tensile strength and impact toughness were 16 MPa and 37 kJ·m-2, respectively. The apparent visconsity of the blend decreased gradually with the increase of the nano-CaCO3 addition at 250 ℃.