Graphene/aluminum metal matrix composites (MMC) with enhanced thermal conductivity are fabricated by friction stir processing (FSP). In fabrication of the MMC, graphene reinforcement is applied in the form of a graphene oxide (GO)/water colloid for safer and simpler processing. The result of Raman spectroscopy suggests that graphene reinforcements are successfully mixed into the aluminum matrix by FSP. The thermal conductivity of the graphene/ aluminum MMC is measured to increase by more than 15% in comparison with that of the aluminum matrix. FSP and graphene reinforcement both improve the ductility of the fabricated MMC.