A combined first-principles and thermodynamic study of the Bi-Cs and Bi-Tm systems has been performed and a self-consistent thermodynamic database has been obtained. The enthalpies of formation of Bi2Cs, Bi4Cs5, Bi2Cs3, BiCs3, BiTm and Bi3Tm5 are computed via density functional theory using the VASP code. The CALPHAD assessment of Bi-Cs and Bi-Tm systems was then performed by considering both the first-principles computed enthalpies of formation and the experimental phase equilibrium data. The liquid phase of the Bi-Tm system was modeled with Redlich-Kister polynomial, while the associate model was used to describe the short-range ordering behavior of the Bi-Cs liquid phase. The six inter-metallics compounds in the two systems are described as stoichiometric phases. An agreement between the calculated results and experimental data was obtained. (C) 2014 Elsevier Ltd. All rights reserved.