Mechanical alloying was used in order to synthesize nanocrystallized ZnSb powder. It has been shown that after 3 h of milling and with an excess of zinc in the mixture of Zn + Sb powder, the ZnSb phase was obtained with crystallites size of 40 nm. This powder was characterized by X-ray diffraction using Rietveld refinement and differential thermal analysis before being sintered by Spark Plasma Sintering. We also present thermoelectric properties of ZnSb and a comparison is made with a solidified ingot of ZnSb. Thanks to our method of synthesis, the electrical properties (power factor) of ZnSb are stable in the temperatures range (300–700 K) and very close to the ones of Zn4Sb3 which is the best thermoelectric material so far in the Zn–Sb system.