A three-dimensional (3-D) structured sensor of microcrystalline beta-PbO2-coated carbon felt consisting of crisscrossing carbon fibers has been developed to determine chemical oxygen demand in wastewater. Each carbon fiber in the felt is coated by perfect octahedral beta-PbO2 microcrystals. The unique structure makes it possess huge surface area and abundant active sites for generating hydroxyl radicals, thus exhibiting excellent performances. Results show a RSD within 5% as compared with the traditional standard method, a high sensitivity of 2.05 x 10(-3) mA cm(-2)/mg L-1, a wide linear range of 50-5000 mg L-1, a correlation coefficient (R) of 0.993 and a detection limit of 3.9 mg L-1 (S/N= 3). Additionally, this electrode demonstrates excellent reproducibility, low cost and good stability. These properties enable the electrode to be used as a COD sensor for in situ determination in industry, showing a promising application perspective. (C) 2015 Elsevier Ltd. All rights reserved.