Nano-CaCO3/polypropylene (PP) masterbatch containing above 80 wt % nano-CaCO3 was prepared by nano-CaCO3 coated PP modified by reactive monomers. The chemical interaction, crystallization and melting behavior, thermal stability, morphology, and surface contact angle of masterbatch were investigated with IR, DSC, TEM, TGA, ESCA, and surface contact angle. The results indicated that nano-CaCO3 was coated by PP graft copolymers in the masterbatch modified by reactive monomers. The graft ratio and crystallization and melting behavior of PP in the masterbatch depended on the type and content of reactive monomer. The crystallization temperatures of masterbatch modified by reactive monomer is methyl methacrylate > butyl acrylate > methyl acrylate-mixture of acrylic acid and styrene > unmodified-maleic anhydride-acrylic acid > styrene. Modification by reactive monomer increased the thermal stability and surface contact angle of masterbatch. (c) 2006 Wiley Periodicals, Inc.