Thermodynamic optimization of the binary Ca-Fe and ternary Ca-Fe-Si systems has been conducted based on the critical evaluation of all phase diagram and thermodynamic properties data available in the literature. The thermodynamics of the liquid solution was described using the Modified Quasichemical Model which takes into account short-range ordering. As a result, a set of model parameters for all solid and liquid phases was produced. With the help of a Gibbs energy minimization routine, any thermodynamic properties and phase diagrams in the ternary system can be calculated. Several pseudo-binary sections and isopleths in the ternary Ca-Fe-Si system were predicted from the present thermodynamic model with optimized model parameters. In addition, Scheil cooling calculations were performed to understand the evolution of as-cast microstructure of metallurgical grade Si (Si-Fe-Ca alloy) depending on its impurity content.