Low-density polyethylene (LDPE) was filled with blends of different proportions of two sizes of calcium carbonate (CaCO3; 600 and 2500 mesh). The torque of the LDPE/CaCO3 samples was measured with a torque rheometer. The results showed that the process torque values of the LDPE/CaCO3 samples obviously decreased when LOPE was filled with a blend of two sizes of CaCO3 (600- and 2500-mesh CaCO3 blend) in comparison with samples filled with CaCO3 of a single size (600 or 2500 mesh). When the ratio of 600-mesh CaCO3 to the total CaCO3 was in the range of 40-60 wt %, the lowest torque value of the LDPE/CaCO3 samples was achieved. When the content of CaCO3 in a sample was 30 wt %, LDPE filled with CaCO3 of different size distributions showed the largest decrease in the torque ratio in comparison with the samples filled with CaCO3 of a single size. The torques of LDPE samples filled with CaCO3 of a single size and those filled with CaCO3 of different size distributions at different temperatures were also studied. The results showed that the flow activation energy and flow activation entropy of LOPE samples filled with CaCO3 of different size distributions increased obviously. The increase in the flow activation entropy was used to explain the phenomenon of the process torque decreasing for LDPE samples filled with CaCO3 of different size distributions. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2408-2416, 2010