The surface modification of nano calcium carbonate (nCaCO(3)) particles was carried out with a soluble compound of lanthanum via a coating process of chemical deposition, and nCaCO(3) particles covered with a compound of lanthanum (nCaCO(3)-La) were prepared. The polypropylene (PP)/nCaCO(3) and PP/nCaCO(3)-La composites were prepared with a two-roll mill. The measurements of the mechanical properties showed that the impact strength of the composites increased at first and then decreased with the addition of fillers, and the tensile strength was reduced at the same time. The impact strength of PP/nCaCO(3)-La was higher than that of PP/nCaCO(3), and the impact strength of PP/nCaCO(3)-5La was three times that of virgin PP. Transmission electron microscopy and scanning electron microscopy showed that nCaCO(3)-La dispersed well in the PP matrix, the size distribution of the particles was uniform, and nCaCO(3)-La adhered to the PP matrix very closely. The crystallization properties of virgin PP and its composites were studied with differential scanning calorimetry and wide-angle X-ray diffraction. The results showed that the M-PP phase easily formed with the addition of the lanthanum compound. In comparison with virgin PP, the addition of nCaCO(3)-La led to a higher crystallization temperature. The size of the crystallites increased with the addition of nCaCO(3)-La, and the nucleation of PP crystalline was also improved. (c) 2005 Wiley Periodicals, Inc.