Two different types of surface modifiers, 3-aminopropyltriethoxysilane and formamide, were applied to carbon black (CB) particles to lower electrical resistivity of polymer composites prepared by treated CB. Two different matrices, low-density polyethylene and nylon 6, were chosen to compound with surface modified CB. Surface energy of CB was increased by adding amine or amide functional groups during surface treatment of CB. According to electron spectroscopy for chemical analysis (ESCA), chemical modification in surface chemistry of CB was obtained with the chemicals used for the treatment due to the nitrogen atoms in their structures, which may act is dopant atom. As a result of this, electrical resistivity of composites prepared by treated CB decreased. In addition, there was not any significant change in tensile strength and tensile modulus of the composites with the surface treatment. (c) 2007 Wiley Periodicals, Inc.