Abstract: The results ever reported about the influence of pH on the oxidation of ascorbic acid (H₂A) were quite different and unreasonable. The main reason for this, we think, is the use of buffers. Different buffers have different effects on the reaction.Instead of using buffers, we used automatic potential titrator to control the pH. In the pH range of 3～10, the rate equation of the Cu (Ⅱ) catalyzed aerobic oxidation of ascorbic acid was determined, and the curve of the rate constant R' against pit was given. From these data, the special rate constants with respect to H₂A, HA^- and A^2- were estimated. The influence of pH on the reaction was discussed.