The thermodynamic data of the Al-Zr, Al-V and Zr-V systems have been obtained from their phase diagram data using the tie line variation method. The binary thermodynamic data have subsequently been used to calculate the binary phase diagrams which are in good agreement with the measured phase diagrams. The calculated binary thermodynamic data and some measured ternary data have been used to calculate isothermal ternary phase diagrams of the Al-Zr-V system at 750 and 1800k.