Nano-calcium carbonate (nano-CaCO3) was used in this article to fill acrylonitrile-butadiene-styrene (ABS)/poly(methyl methacrylate) (PMMA), which is often used in rapid heat cycle molding process (RHCM). To achieve better adhesion between nano-CaCO3 and ABS/PMMA, nano-CaCO3 particles were modified by using titanate coupling agent, aluminum-titanium compound coupling agent, and stearic acid. Dry and solution methods were both utilized in the surface modification process. ABS/PMMA/nano-CaCO3 composites were prepared in a corotating twin screw extruder. Influence of surface modifiers and surface modification methods on mechanical and flow properties of composites was analyzed. The results showed that collaborative use of aluminum-titanium compound coupling agent and stearic acid for nano-CaCO3 surface modification is optimal in ABS/PMMA/nano-CaCO3 composites. Coupling agent can increase the melt flow index (MFI) and tensile yield strength of ABS/PMMA/nano-CaCO3 composites. The Izod impact strength of composites increases with the addition of titanate coupling agent up to 1 wt %, thereafter the Izod impact strength shows a decrease. The interfacial adhesion between nano-CaCO3 and ABS/PMMA is stronger by using solution method. But the dispersion uniformity of nano-CaCO3 modified by solution method is worse. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2520-2528, 2013