In order to develop new functional biomaterials, the Zr Au alloy system was focused and a Zr 9 molAu near eutectoid alloy was used in this work. Effect of solution treatment and aging treatment temperatures on phase constituent, microstructure and Vickers hardness was investigated. It was found that Zr 9 molAu is a hypereutectic composition and experimental results in this work are not in agreement with the experimental phase diagram reported by Lomello Tafin et al., but in good agreement with the calculated phase diagram reported Su et al. The major apparent phase was hcp aZr regardless of the heat treatment condition and Zr 3 Au second phase precipitated when heat treated at 1173 K or lower temperatrues. The Vickers hardness value was HV503 after the solution treatment at 1273 K, but became lower with increasing the amount of micrometer size Zr 3 Au precipitates. The hardness of this alloy was mainly due to the amount of the solute Au in aZr matrix. However, the alloy was slightly hardened by aging at 673 K due to the formation of submicron meter size fine Zr 3 Au precipitates.