Effects of the surface modi. cation of multi-walled carbon nanotubes (MWCNTs) by surfactant, hexadecyltrimethylammonium bromide ( CTAB) and coupling agent, gamma-aminopropyltriethoxy silane ( KH550), on the microstructure and electrical properties of rubber composites loaded with MWCNTs were studied. The results show that the CATB can improve the dispersion of MWCNTs, but it cannot improve the interfacial interaction remarkably between MWCNTs and rubber. While the use of KH550 is benefit of the dispersion of MWCNTs and induces the strong interfacial interaction, which often hinders electron transport in the composites. These results are further confirmed by the temperature and pressure dependencies of the electrical properties of the composites. (c) 2008 Elsevier B. V. All rights reserved.