Cytochrome oxidase [EC 1.9.3.1] was isolated and purified from ETP**** of Sacchromyces oviformis M2 by means of cholate and ammonium sulfate extraction and ammonium sulfate fractionation. The purified preparation contained approximately 7—8 mμwnoles heme a and copper per mg. protein. The activity of the purified preparation was about 20 fold more than that of ETP. The optimum pH was found at 6.2 and the optimum phosphate buffer concentration was 67 mM. The Km value of cytochrome c was 2—4×lO−6M. The maximum turnover number of the purified preparation was about 14,000 which was 10 fold higher than that of a beef heart preparation. Based on the above results together with other properties, the properties of cytochrome oxidase of baker's yeast were discussed.