The distribution of a filler in a polymeric matrix is one of the most important factors affecting the physical properties of the final product. For this reason, the main objective of this study was to introduce aluminum oxide (Al2O3), acting as a dispersing agent, to reduce the filler-filler interaction and enhance the filler-polymer interaction. To achieve this aim, the electrical behavior of a styrenated polyester resin filled with different amounts of high-abrasion furnace black in the presence of 5% Al2O3 was studied in the vicinity of the percolation threshold to evaluate the effect of the addition of Al2O3 in an attempt to reduce the filler-filler interaction through the polyester matrix. At a certain concentration of carbon black, an abrupt increase was noticed through electrical conductivity, permittivity, and dielectric loss investigations. With this increase, the tendency of conductive chain formation increased through the aggregation of a carbon black particle network. The addition of 5% Al2O3 improved the filler distribution by lowering the aggregate size and consequently enhanced the formation of the network. From the Arrhenius temperature dependence of the electrical conductivity, the activation energy and pre-exponential factor were obtained, and they confirmed the validity of the compensation law for the semiconducting composite systems. The composites were also analyzed by thermogravimetric analysis. Al2O3 improved the thermal stability of the composites in comparison with that of a sample free of Al2O3. (c) 2008 Wiley Periodicals, Inc.