The influences of Cu additions on the microstructural evolution and room-temperature tensile properties of the as-cast CrFeCoNi were investigated in detail. The results revealed that the structure of the alloy changed from a FCC single-phase to FCC1 plus FCC2 dual-phase by adding Cu element. The FCC2 phase was determined to be Cu-rich phase existing in the inter-dendrite region, and its volume fraction increased with the increase of Cu additions. The formation of Cu-rich inter-dendrite was mainly ascribed to the liquid-phase separation induced by the large positive mixing enthalpy between Cu and other metallic elements. The yield and ultimate tensile strengths against the Cu content displayed a positive correlation due to the enhancement of short-range obstacles to dislocations slip, while the more significant superposition of stress field produced by the dislocation piling-ups at grain boundaries of Cu-containing high-entropy alloys led to a small fracture strain.