With the capacity of energy conversion from heat to electricity directly, thermoelectric materials have been considered as an altative solution to global energy crisis. In this work, Cu modified Bi0.5Sb1.5Te3 (BST) composites are prepared by a facile electroless plating Cu method, spark plasma sintering, and annealing. The annealed 0.22wt.％Cu/BST has an enhanced peak Figure of Merit (zT) of ～ 0.71 at 573 K with high average zT of 0.65 in the wide temperature range between 300 and 573 K. Due to the significant increase of electrical conductivity and low lattice thermal conductivity, the annealed 0.22wt.％Cu/BST shifts peak zT to high temperature,and shows 492％ enhancement than that of pristine BST with zT of 0.12 at 573 K. Through detailed structural characterization of the annealed 0.22wt.％Cu/BST, we found that Cu can dope into BST matrix and further form Cu2Te nanoprecipitates, dislocations, and massive grain boundaries, leading to a low lattice thermal conductivity of 0.30Wm?1 K?1 in the annealed 0.22wt.％Cu/BST. Such enhanced peak zT in high-temperature and high average zT in the wide temperature range shows that the electroless plating Cu method and annealing can improve the thermoelectric performance of commercial BST and expand the applicability of Bi2Te3 thermoelectric materials in the power generations.