Sn-Sb-Se alloys are chalcogenide materials of various promising application, but there are only few phase equilibrium data of the Sn-Sb-Se ternary system. The liquidus projection and 400oC isothermal section of the Sn-Sb-Se ternary system are determined in this study. Sn-Sb-Se alloys are prepared. The primary solidification phases of the as-cast alloys and equilibrium phases of the equilibrated samples are determined. There are eleven primary solidification phases: Sn, Sb, Se, Sb2Sn3, SbSn, Sb2Se3, SnSe, SnSe2, SnSbSe2, Sn2Sb9Se9, and SnSb2Se4. Additionally, there are two miscibility gaps along Sn-Se and Sb-Se sides. There are eleven invariant reactions in the Sn-Sn-Se ternary system, and that of the lowest reaction temperature is L=SnSe+Sb2Se3+Se at 221±5oC. There are eleven tie-triangles, which are Liquid+SbSn+SnSe, SbSn+SnSe+Sb, SnSe+Sb+Sn2Sb9Se9, Sb+Sb2Se3+Sn2Sb9Se9, SnSe+Sn2Sb9Se9+SnSbSe2, Sb2Se3+Sn2Sb9Se9+SnSb2Se4, Sn2Sb9Se9+SnSbSe2+ SnSb2Se4, SnSe+SnSbSe2+SnSb2Se4, SnSe+SnSe2+SnSb2Se4, SnSe2+Sb2Se3 +SnSb2Se4, and SnSe2+Liquid+Sb2Se3.