CaCO3/acrylonitrile-butadiene-styrene (ABS) and CaCO3/ethylene-vinyl acetate copolymer (EVA)/ABS nanocomposites were prepared by melting-blend with a single-screw extruder. Mechanical properties of the nanocomposites and the dispersion state of CaCO3 particles in ABS matrix were investigated. The results showed that in CaCO3/EVA/ABS nanocomposites, CaCO3 nanoparticles could increase flexural modulus of the composites and maintain or increase their impact strength for a certain nano-CaCO3 loading range. The tensile strength of the nanocomposites, however, was appreciably decreased by adding CaCO3 nanoparticles. The microstructure of neat ABS, CaCO3/ABS nanocomposites, and CaCO3/EVA/ABS nanocomposites was observed by scanning electron microscopy. It can be found that CaCO3 nanoparticles were well-dispersed in ABS matrix at nanoscale. The morphology of the fracture surfaces of the nanocomposites revealed that when CaCO3/EVA/ABS nanocomposites were exposed to external force, nano-CaCO3 particles initiated and terminated crazing (silver streak), which can absorb more impact energy than neat ABS. (c) 2007 Wiley Periodicals, Inc.