PVC/Blendex/Nano-CaCO3 composites were prepared by melt-blending method. The Blendex (BLENDEX(R) 338) (GE Specialty Chemicals Co., Ltd., Shanghai, China) was an acrylonitrile-butadiene-styrene copolymer with high butadiene content. The fracture behavior of PVC/Blendex/nano-CaCO3 composites was studied using a modified essential work of fracture model, U/A = u(0), + u(d)l where u(0) is the limiting specific fracture energy and u(d), is the dissipative energy density. The u(0) of PVC/Blendex blend could be greatly increased by the addition of nano-CaCO3 while the u(d) was decreased. Nano-CaCO3 with particle size of 38 nm increased the u(0) of PVC/Blendex blend more effectively than that with particle size of 64 nm, when nano-CaCO3, content was below 10 phr. Both the u(0) and u(d) of PVC/Blendex/nano-CaCO3, composites were not much affected by increasing specimen thickness from 3 mm to 5 mm, while the two fracture parameters were increased with increasing loading rate from 2 mm/min to 10 mm/min, and u(d) was found to be more sensitive to the loading rate than u(0). (C) 2004 Wiley Periodicals, Inc.