In the Zn-Sn-Sb ternary system, Zn 4Sb 3, ZnSnSb 2, and ZnSb have attracted attentions as advanced thermoelectric materials. Zn-Sn-Sb based alloys with various compositions were fabricated and the thermoelectric properties were investigated. That system is composed by orthorhombic ZnSb phase, tetragonal ZnSnSb 2 phase with chalcopyrite structure, and rhombohedral SnSb phase. Large Sn content increases volume fraction of the metallic SnSb phase, which degenerate the powar factor. The ZnSb based alloy shows relatively large Seebeck coefficient. Sn substitution for ZnM xSb 1-x significantly enhances the power factor, which indicates that Sn is effective dopant for ZnSb. © 2011 Materials Research Society.