Homogeneous　magnesium　alloy　(ZK60)　reinforced　by　low　content　of　graphene　nanoplatelets　(GNPs)　was　fabricated　by　facile　melt　stirring　and　hot　extrusion　processes　with　cost　effectiveness.　GNPs　were　pre-dispersed　with　Mg　powder　and　extruded　into　rods　used　as　precursor　for　melting,　which　effectively　guaranteed　the　integrity　and　dispersion　of　GNPs.　In　composites,　GNPs　closely　combined　with　the　magnesium　matrix　in　nanoscale.　Compared　with　ZK60　alloy,　the　composite　with　only　0.05　wt%　GNPs　can　perform　62%　enhancement　in　yield　strength　up　to　256　MPa,　exhibiting　an　ultra-high　strengthening　efficiency　of　1550.　Based　on　theoretical　analysis,　load　transfer　of　GNPs　contributed　most　(similar　to　72%)　to　the　strength　improvement　of　GNP/ZK60　composite,　due　to　the　2D　interfacial　contacting　and　continuous　combination　of　GNPs　with　matrix.　This　study　explored　the　strengthening　potential　and　mechanism　of　GNPs　in　metal　matrix　composites　with　insight　of　scale-up　fabrication.