The particle surface of nanometer calcium carbonate (nano-CaCO3) was treated by fatty acid and titanate coupling agent, and polypropylene (PP) composites filled with nano-CaCO3 with the volume fraction range from 0 to 3.0% were prepared by means of melt blending in a twin-screw extruder. The V-notched impact strength of the nanocomposites was measured at room temperature. The V-notched impact fracture surface fractal dimensions of PP/nano-CaCO3 composites were measured by means of projective-covering method, and the relationship between the fracture surface fractal dimension and the impact strength of these composites was investigated. The results showed that the fracture surface fractal dimension ranges from 2.367 to 2.412, all of the correlation coefficients were higher than 0.96, the strong correlation indicated that the fracture surface of the composites was fractal obviously, and the relationship between the impact strength and fractal dimension of the composites obeyed roughly exponential function. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 31: 7181, 2012; View this article online at . DOI 10.1002/adv.20237