Phase relation and mechanical property of Cr2Zr Laves phase alloy systems were investigated in terms of ternary alloying based on geometric concept of atomic sizes of constituent alloying elements. Ternary phase diagrams at 1573 K of Cr-Zr-Nb and Cr-Zr-Hf alloy systems were examined using SEM-EPMA analysis in order to understand the site occupation behavior of ternary elements and the phase stability of Laves phase. In the Cr-Zr-Nb alloy system, Laves phase had a broad off-stoichiometry range in the middle of Cr2Zr-ZrNb2 pseudo-binary line, while a limited and uniform range of Laves phase field was found in the Cr-Zr-Hf alloy system. For both Laves phase alloys, 0.2% offset yield strength decreased with increasing content of allying element, on the other hand compressive ductility increased with increasing content of alloying elements. Details will be discussed in conjunction with microstructure, phase stability and atomic size considerations.