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　OK　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.　(C)　2013　Elsevier　B.V.　All　rights　reserved.