Carbon nanofibers(CNFs) and Carbon nanotubes(CNTs) are expected to be fillers of polymer matrix composites. We have measured thermal conductivity of polypropylene(PP) matrix composites filled with vapor grown carbon fibers (VGCFs) and vaper grown carbon nanofibers(VGNFs). Specimens were fabricated by injection molding with changing the concentration of the fillers in the composites from 0 to 50wt%. Thermal conductivity increased with increasing the filler concentration and the value of 3.46W/mK was obtained when VGCF concentration was 50wt% with highly oriented along measuring direction of thermal conductivity. This value is approximately seventeen fold higher than that of the pure PP(0.20W/mK).