Elemental aluminum (Al) powders reinforced with 1-10 wt% of ultra-dispersed nanodiamond (UDD) powders were ball-milled in a Spex (TM) Mixer/Mill between 0 and 120 min followed by consolidation and sintering. X-ray diffraction analyses on the ball-milled powders revealed only alpha-Al peaks, whereas Al4C3 phase was identified along with alpha-Al in all sintered composites. Increasing the addition of nanodiamond to Al-matrix resulted in improved hardness of both ball-milled and sintered composites. The wear resistances of the Al-UDD composites were significantly improved with increasing UDD contents. Under similar load and sliding conditions, the wear resistance of Al matrix composite containing 10 wt% nanodiamond enhances about 40 times when compared with unreinforced aluminum.