Graphite nanofibers (GNFs) reinforced aluminum matrix composites have been fabricated successfully by powder metallurgy methods. The GNF-Al mixtures were prepared through ultrasonication and ball milling. The GNF-Al composites were consolidated by hot isostatic pressing (HIP) and then a high density of compacts could be obtained. The microstructure and the distribution of nanofibers in matrix material were investigated by microscopy observations. A uniform distribution of nanofibers in aluminum matrix was obtained. The mechanical properties were measured by microhardness and compression tests. The optimal contents of nanofibers were determined in view of the mechanical properties. The results of thermal tests indicate that the addition of nanofibers were enhanced the thermal conductivity but, the dimensional stability such as thermal expansion was not improved significantly.