A photoelectrochem. probe for rapid detn. of COD is developed using a nanostructured mixed-phase TiO2 photoanode, namely PeCOD probe. A UV-LED light source and a USB mircroelectrochem. station are powered and controlled by a laptop computer, which makes the probe portable for onsite COD analyses. The photoelectrochem. measurement of COD was optimized in terms of light intensity, applied bias, and pH. Under the optimized conditions, the net steady state currents originated from the oxidn. of orgs. were found to be directly proportional to COD concns. A practical detection limit of 0.2 ppm COD and a linear range of 0-120 ppm COD were achieved. The anal. method using the portable PeCOD probe has the advantages of being rapid, low cost, robust, user-friendly, and environmental friendly. It was used to det. the COD of the synthetic samples consisting of K hydrogen phthalate, D-glucose, glutamic acid, glutaric acid, succinic acid, and malonic acid, and real samples from various industries, such as bakery, oil and grease manufacturer, poultry, hotel, fine food factory, and fresh food producer, com. bread manufacturer. Excellent agreement between the proposed method and the conventional COD method (dichromate) was achieved.