The Zintl compound Mg3Sb2 has been recently identified as promising thermoelectric material owing to its high ther-moelectric performance and cost-effective, nontoxicity and environment friendly characteristics. However, the intrinsically p-type Mg3Sb2 shows low figure of merit (zT =0.23 at 723 K) for its poor electrical conductivity. In this study, a series of Mg3?x Lix Sb2 bulk materials have been prepared by high-energy ball milling and spark plasma sintering (SPS) process. Electrical transport measurements on these materials revealed significant improvement on the power factor with respect to the undoped sample, which can be essentially attributed to the increased carrier concentration, leading to a maximum zT of 0.59 at 723 K with the optimum doping level x=0.01. Additionally, the engineering zT and energy conversion efficiency are calculated to be 0.235 and 4.89％, respectively. To our best knowledge, those are the highest values of all reported p-type Mg3Sb2-based compounds with single element doping.