A novel rapid methodology for the determination of chemical oxygen demand (COD) based on photoelectrochemical oxidative degradation principle (PECOD) was proposed and experimentally validated. With this new method, the extent of degradation of dissolved organic matter in a water sample is measured simply by directly quantifying the extent of electron transfer at a TiO2 nanoporous film electrode during an exhaustive photoelectrocatalytic degradation of organic matter in a thin layer photoelectrochemical cell. The PECOD method demonstrated in this work is a direct and absolute method. It does not require the use of standard for calibration. The method, in principle, measures the theoretical COD value due to the extraordinary high oxidation efficiency and accuracy of charge measurement. This new approach overcomes many of the current problems associated with existing oxygen demand techniques (e.g., the matrix effect, one of the serious practical problems that most rapid COD methods suffered because of the insufficient oxidation efficiency). The PECOD method overcomes the matrix effect by employing a highly effective photoelectrochemical system that is capable of fully oxidizing a wide spectrum of organics in the water sample. The method was successfully applied to determine the COD of a range of synthetic and real samples. Excellent agreement with a standard dichromate method was achieved. The practical detection limit of 0.2 mg L-1 COD with the linear range of 0-200 mg L-1 was also achieved. The PECOD method is a method that is environmentally friendly, robust, rapid, and easily automated. It requires only 1-5 min to complete an assay and consumes very limited reagent (electrolyte only).