The effects of CaCO3 on the crystallization behavior of polypropylene (PP) were studied by means of DSC and WAXD．The average sizes of the CaCO3 powders used were 0.1 μm (UC) and 0.5μm (Gc)

respectively．The PP／CaCO3 composites at compositions of 1 phr and 10 phr were investigated．The results showed that the addition of CaCO3 reduced the supercooling

the rate of nucleation and the overall rate of crystallization (except for the 10 phr UC/PP sample)．The crystallinity of PP was increased and the size distribution of the crystallites of α-PP was broadened．On the other hand

the crystallization rate of 10 phr UC／PP is 1.5 times higher than that of neat PP．It has an overall rate of crystallization 2 times as much as that of the neat PP and has the maximum crystallinity．The sizes of crystallites and the unit cell parameters of α-PP were varied by the addition of CaCO3．β-PP was formed by addition of GC and was not detected by addition of UC．The differences of crystallization behaviors of PP might be attributed to the combined effects of the content and size of CaCO3 filled．