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Copper matrix composites reinforced with graphene nanoplatelets (GNPs) were prepared by low-energy ball milling and spark plasma sintering (SPS). The effects of graphene content on the microstructure and the properties of such composites were studied. The results show that as the graphene content increases, the mechanical properties of the composite first improve and then gradually deteriorate. When the graphene content is 0.25wt%, the ultimate compressive strength of the composite is 409 MPa and its electrical conductivity is as high as 90% International Annealed Copper Standard (IACS). Further addition of graphene in the composite produces a larger cluster of GNPs within the copper matrix and results in the deterioration of the aforementioned properties. However, as the graphene content continues to increase, the wear rate of the composite declines steadily. The uniform distribution of graphene amongst the copper particles enables the transformation of the external applied load from the copper matrix to the chromium particles and graphene, effectively blocking internal dislocation motion, and thus improving the strength and other tribological properties of the composites.