To　improve　the　effectiveness　of　high　entropy　alloys　(HEAs)　as　reinforcing　agents　in　metal　matrix　composites,　the　10　vol.%　HEA/Cu　composite　was　fabricated　by　spark　plasma　sintering,　followed　by　different　holding　time　at　850　°C　and　hot　extrusion.　The　as-extruded　composites　were　examined　by　microstructural　characterization　using　scanning　electron　microscopy,　electron　probe　microanalysis　and　transmission　electron　microscopy　along　with　performance　tests.　The　results　show　that　the　preheating　at　850　°C　promotes　the　diffusion　of　Al,　Co,　Cr　Fe　and　Ni　from　the　reinforcement　to　Cu　matrix,　along　with　the　diffusion　of　Cu　towards　reinforcement,　which　give　rise　to　the　formation　of　core-shell　structure　at　less　than　6　h.　However,　such　core-shell　structure　is　invisible　once　the　preheating　time　is　above　6　h.　At　less　than　6　h,　the　increased　yield　strength　of　the　HEA/Cu　composite　can　be　ascribed　to　the　solid　solution　strengthening　of　Cu　matrix　stemmed　from　element　diffusion,　whereas　the　improved　plasticity　is　due　to　the　increasing　shell　thickness　in　reinforcements　with　the　preheating　time.　At　above　6　h,　the　strengthening　effect　of　reinforcements　decreases　significantly,　giving　rise　to　the　decrease　in　the　yield　strength　and　the　improvement　in　the　plasticity.　©　2020　Elsevier　Ltd