Based　on　the　available　experimental　data,　the　Bi-Er　and　the　Bi-Dy　binary　systems　have　been　assessed　thermodynamically　using　the　CALPHAD　(CALculaton　of　PHAse　Diagram)　technique.　The　formation　enthalpies　at　0　K　of　the　compounds,　Bi3Er5,　BiEr,　Bi3Dy5　and　BiDy,　were　calculated　by　the　first-principles　method　and　Birch-Murnaghan　equation　of　state,　and　the　calculated　results　were　used　in　the　present　thermodynamic　optimization.　All　these　compounds　in　the　Bi-Er　and　the　Bi-Dy　systems　were　treated　as　stoichiometric　compounds.　The　liquid　phase　was　modeled　as　a　substitutional　solution　phase　based　on　random　mixing　of　the　constituent　atoms　and　the　excess　Gibbs　energy　was　formulated　with　the　Redlich-Kister　polynomial.　Good　agreements　were　obtained　between　the　calculated　results　and　the　experimental　data　for　both　the　thermochemical　properties　and　the　phase　equilibrium　relations.　©　2013　Elsevier　B.V.　All　rights　reserved.