Abstract: We found that the photochemical reaction of dilute vitamin C solution is zero order at stirring. While nonstirring using a HP-8451 spectrophotometer have been able to record decay and regular periodic oscillations on certain concentration range and nearby 25 ℃. It is shown that these oscillations, however, will appear preperiod which is more than 1200 sec after the start of the irradiation. The main oscillating periodsare 117±6 sec and the largest amplitude is 0.035 Abs. In this paper the effects of concentration, temperature and stirring on the photochemical oscillation are investigated, and the possible mechanism of photochemical reaction in dilute vitamin C solution and of forming photochemical oscillation are proposed and discussed. Until now there are no reported on it.