The phase diagrams of Yb-Cd and Yb-Sn systems were calculated by coupling the CALPHAD method and ab initio calculations. The enthalpies of formation of nine binary compounds (YbCd, alpha YbCd2, Yb2Sn, alpha Yb5Sn3, beta Yb5Sn3, Yb5Sn4, YbSn, Yb3Sn5 and YbSn3) were determined via ab initio density functional theory using the VASP code. Based on the available experimental data and the computed enthalpies of formation of the compounds, a thermodynamic assessment was carried out. The liquid phases and the gamma Yb(bcc) and beta Yb(fcc) solid solutions were described by the Redlich-Kister polynomial model, while all the intermetallic compounds were treated as stoichiometric phases. A set of optimized model parameters were obtained for Yb-Cd and Yb-Sn systems. The calculated phase diagrams of these binary systems and their thermodynamic properties are presented and compared with the experimental data.