Critical evaluation and optimization of all available phase diagrams and thermodynamic data for the Mn-RE (RE = Tb, Dy, Ho, Er, Tm, and Lu) systems has been conducted to obtain reliable thermodynamic functions of all the phases in the systems. Key experiments for the Mn-Dy system were performed using DSC and solution calorimeter. In the thermodynamic modeling, it is found that the Mn-RE systems show systematic changes in the phase diagrams and thermodynamic properties such as enthalpy of mixing in liquid state in the order of periodic number in the lanthanide series. The systematic thermodynamic modeling approach for RE elements allow to resolve inconsistencies in the experimental data and estimate unknown thermodynamic properties and phase equilibria of Mn-RE system.