1. The oxidation velocity of the mixture of sodium sulphite and stannous chloride in alkaline solution with air was studied. 2. When the initial concentration of stannous chloride is not small, the oxidation velocity is independent of their concentrations and is smaller than that of each. 3. When the initial concentration of stannous chloride is small, the oxidation of the mixture takes place at a slow rate first, and increases with time.