The In–Pt–Sb system is modeled using the CALPHAD technique. The solution phases (liquid, fcc(Pt), rhom(Sb) and tetra(In)) are described as substitutional solution. The enthalpies of formation of the intermetallic compounds, Pt 7 Sb, Pt 3 Sb, Pt 3 Sb 2 , PtSb, PtSb 2 are calculated using first-principles calculations. In the In–Pt–Sb system, the compounds In 3 Pt 2 , In 2 Pt, In 7 Pt 3 in the In–Pt binary system and the compounds PtSb 2 and PtSb in the Pt–Sb binary system are treated as line compounds (In,Sb) m Pt n according to experimental solid solubility of the third component. The compound In 5 Pt 6 is treated as (In,Pt,Sb) 5 (In,Pt) 6 based on its thermodynamic model in the In–Pt system and experimental solid solubility of Sb in the In–Pt–Sb system. The thermodynamic model of compound InPt 3 keeps the order–disorder transition model with fcc(Pt) solid solution which was used in the In–Pt binary system, and is treated as (In,Pt,Sb) 0.25 (In,Pt,Sb) 0.75 . Other compounds InPt, In 9 Pt 13 , αIn 2 Pt 3 , βIn 2 Pt 3 , InPt 2 and InSb in the In–Pt–Sb system keep the same thermodynamic models as those in binary systems. Based on the published experimental isothermal sections, vertical sections and the liquidus surface projection, the In–Pt–Sb system is modeled, and a set of self-consistent thermodynamic parameters is obtained.