Zn–Sb based alloys with Cu 2 Sb addition were prepared using spark plasma sintering technique and the effects of a Cu-contained intermetallic phase on the microstructures and thermoelectric properties were examined. Rietveld refinement reveals that there are many phases in the alloys, which involve β-Zn 4 Sb 3 , a major phase ZnSb, a small amount of an intermetallic compound Cu 5 Zn 8 and unidentified impurity phases, the quantities of ZnSb and Cu 5 Zn 8 increase from 67.3wt.% to 91.8wt.% and 0–4.3wt.% with Cu 2 Sb additive increasing, respectively. The ZnSb plays a fundamental role in controlling the thermoelectric properties, and Cu 5 Zn 8 is of great significance to optimize the transport properties. The maximum thermoelectric figure of merit ZT of 0.72 is obtained for the alloy (Cu 2 Sb) 0.05 –(Zn 4 Sb 3 ) 0.95 at 654K, which is 0.25 higher than that of undoped β-Zn 4 Sb 3 at the same conditions. Therefore, we conclude that a proper addition of Cu 2 Sb can contribute to the improvement of thermoelectric properties of Zn–Sb based alloys.