The nano-CaCO3/Acrylonitrile-Butadiene-Styrene (ABS) composites were prepared by melting-blend with the single-screw extruder. The mechanical properties of the nanocomposites and the dispersion of nano-CaCO3 were investigated by means of transmission electron microscopy (TEM) and mechanical tests. The micro structure of the fracture section of the nanocomposites was analyzed by means of scanning electron microscopy (SEM). The results show that not only the impact property but also the rigidity property and the bending modulus of the system have been increased evidently by added modificated nano-CaCO3. However, the tensile strength of the nano-composites has a little decreased by added the modificated nano- CaCO3. The modificated nano-CaCO3 has been dispersed well in the matrix in the nanometer scale. The micro structure of the fracture section of the nanocomposites proved that when the composites have been impacted, the modificated nano-CaCO3 particles have taken an action of initiating and terminating crazing (silver streak), which can absorb more impact energy than the pure ABS resin. Compared with the pure ABS resin material, the notched impact strength of the nano-CaCO3/ABS composites added 2 percent hundred resin (PHR) modificated nano-CaCO3 reach 36.77 kJ/m2, which have been increased up to 44%. At the same time, the rigidity of the nanocomposites has also been enhanced by 23.5% which is increased from 28.16N to 34.87 N.