Abstract: The electrochemical oxidation of thiosulfate on platinum electrode was investigated by cyclic voltammetry. The results of experiments indicate that the behavior of electrochemical oxidation of thiosulfate depends on the pH and scan rate. When the pH value is 5 or 6, the cyclic voltammograms show three oxidation peaks at about 0.05 V, 0.58 V, and 1.02 V. With increasing pH value and decreasing the scan rate, the first oxidation peak becomes vary clear at about 0.05 V. Moreover the potential and the current of peaks have linear relationship with the logarithm and the square root of scan rate, respectively. When the pH value is 8~9, there are three obvious oxidation peaks at about 0.05 V, 0.91 V, and 1.22 V. The curves of cyclic voltammogram are crossed when decreasing the scan rate, and the system exhibits obvious electrochemical oscillations. But when the pH is over 10, the third oxidation peak disappears. The behavior of electrochemical oxidation of thiosulfate is very complicated and the mechanism varies along with the pH of the system.