Using a self-made Pd/C gas-diffusion electrode as the cathode and a Ti/IrO2/RuO2 anode, the degradation of diethyl phthalate (DEP) has been investigated in an undivided electrolysis device by electrochemical oxidation processes. Hydroxyl radical (HO center dot) was determined in the reaction mixture by the electron spin resonance spectrum (ESR). The result indicated that the Pd/C catalyst in Pd/C gas-diffusion electrode system accelerated the two-electron reduction of fed O-2 to H2O2, which is in favor of producing HO center dot. Additionally, the percentage removal of DEP and COD reached about 80.9 and 40.2% after 9 h electrolysis. respectively. It suggested that most of DEP were oxidized to intermediates using the Pd/C gas-diffusion electrode. Furthermore, the ratio of BOD5/COD of resulted solutions was three times larger than the initial ones. Hence, the electrochemical oxidation enhanced the biodegradation character of the DEP solution. Finally, main aromatic intermediates (e.g., monoethyl phthalate (MEP) and phthalic acid (PA)) and main aliphatic carboxylic intermediates (e.g., formic, mesoxalic, oxalic. malonic, succinic, maleic, dodecanoic, and hexadecanoic acids) were identified by GC-MS. Moreover, a reaction scheme involving all these intermediates was proposed. (C) 2010 Elsevier B.V. All rights reserved.