The　Mg2Si-based　materials　have　been　regarded　as　the　promising　and　environment-friendly　thermoelectric　materials　at　the　middle　temperature.　In　this　paper,　the　n-type　Mg-2(Si0.4Sn0.6)Sb-x　(0　＜=　x　＜=　0.02)　solid　solutions　were　successfully　obtained　by　twice　mechanical　alloying　(MA)　and　spark　plasma　sintering　(SPS)　process,　namely　the　method　twice　MA　+　SPS.　This　work　revealed　that　the　dimensionless　figure　of　merit　ZT　was　significantly　enhanced　due　to　the　nanophase　uniformly　dispersed　in　the　fine-grained　and　the　increase　of　the　grain　boundaries　reducing　the　lattice　thermal　conductivities.　Meanwhile,　the　nano-structuring　and　Sb-doping　improved　electrical　performance　for　Mg-2(Si0.4Sn0.6)Sb-x　(0　＜=　x　＜=　0.02)　samples.　The　highest　ZT　value　up　to　1.40　at　673　K　was　obtained　for　Mg-2(Si0.4Sn0.6)Sb-0.018　sample.　(C)　2016　Elsevier　B.V.　All　rights　reserved.