Epoxy/graphite nanoplatelets (GNPs)/carbon black (CB) composites were prepared by liquid mixing method. The morphologies and microstructures of the composites were examined by scanning electron microscope and X-ray diffraction. The results indicated that CB can improve effectively the dispersion of GNPs and form excellent conductive network in the matrix. When the weight ratio of GNPs to CB was 9:1 (total filler content was I wt%), the conductivity of the composite was three orders of magnitude higher than that of composites with GNPs alone (1 wt%). The percolation threshold of GNPs(0.9)CB(0.1)/epoxy resin composites was 0.5 wt. %, which was lower than that of composites with GNPs alone (1 wt%). The mechanism for the effect of CB on electrical property of GNPs/epoxy resin composites was also investigated. POLYM. ENG. SCI., 49:2041-2045, 2009. (C) 2009 Society of Plastics Engineers