A COD measurement by a photocatalytic oxidation method using nano-TiO(2) film was investigated. K(2)Cr(2)O(7) was added into the solution to enhance the efficiency of photocatalytic degradation, and simultaneously K(2)Cr(2)O(7) was reduced to Cr(III) by photogenerated electrons, which were adsorbed on the surface of TiO(2). The measuring principle was based on direct determination of Cr(III) concentration which was proportional to the COD value. Under the optimized experiment condition, the application range was 20-500 mgl(-1), and the detection limit was 20 mgl(-1). The immobilization of photocatalyst on the supports could not only solve the problem of low recovery of the catalyst and hard separation from the solution, but also overcome its shortcoming of poor stability. Applied this method to the determination of real samples, it was found to be rapid and environmentally friendly. Additionally, the method proposed above for determination of COD was in excellent correspondence with values obtained by using the conventional method.