<p>Recently, the demand for improved efficiency of combustion engines is rising with the strict emission constraint. Therefore the requirement for heat resistance is increasing for materials used for springs in automobile exhaust system because the exhaust gas temperature becoming higher.</p><p>Co-W-Al alloys precipitation-strengthened with the γ' phase have good high temperature strength and considered to have potential for higher temperature application than conventional Ni base super-alloys.</p><p>However, for coil spring application, materials must have enough workability in hot and cold roll to make coil wire. In order to enhance hot workability and high temperature mechanical properties, Ni and Cr were added and the optimization was performed in the chemical composition of Co-Ni-Cr-W-Al alloy. In this article, optimization of chemical composition, and relaxation property of coil spring of the developed "COWALOY<sup>®</sup>" are reported.</p>