Some physical and chemical properties of urate oxidase (EC 1. 7. 3. 3) isolated from the cells of Candida utilis were investigated. The molecular weight was estimated to be 1.2×105 by the equilibrium sedimentation and gel filtration methods. The isoelectric point was determined as 5.4 by the method of density electrofocusing. The enzyme showed a slight absorption at 410mμ, and the absorbancy at this wave length was only 3% of that at 280mμ. Contrary to urate oxidase from swine liver, the enzyme from yeast contained a negligible amount of copper, but it contained iron of nearly one atom per mole of the enzyme protein. The yeast urate oxidase was not inactivated by some chelators. However, it was easily inactivated with certain heavy metal ions such as Hg2+, and the inactivated enzyme was reactivated by the addition of thiols, indicating that the enzyme is a sulfhydryl enzyme. The inactivation of the enzyme with urea, on the other hand, was greatly accelerated by the addition of thiols, and some discussion was added to the results obtained.