Vapor-grown carbon fibers (VGCFs) were exposed to a series of chemical treatments and to electro-chemical deposition of copper to modify their surface conditions and alter their electrical properties. The fibers were then mixed with polypropylene using a Banbury-type mixer obtaining composites up to 5 wt % VGCFs. Rheological, electrical, and mechanical properties were evaluated and compared to unfilled polypropylene processed in a similar manner. The composites made with HNO3-treated VGCFs showed a lower electrical resistivity compared to the untreated samples. The composites containing VGCFs subjected to the copper electrodeposition process showed the lowest resistivity with no change in the mechanical proper-ties. Changes in rheological properties demonstrated the effects of varying surface conditions of the VGCFs. Microscopic analysis of these composites showed a heterogeneous distribution of VGCFs forming an interconnected network with the presence of copper on the surface of the VGCFs and in the matrix. Both the interconnected network and the presence of copper led to a lower percolation threshold than those seen in a previous work where high dispersion was sought. (C) 2003 Wiley Periodicals, Inc.