The mineralization of an azo dye Acid Red 14 (AR14) by the photoelectro-Fenton (PEF) process was studied in an undivided electrochemical reactor with a RuO2/Ti anode and an activated carbon fiber (ACF) cathode able to electrochemically generate H2O2. Anodic oxidation and UV irradiation of AR14 were also examined as comparative experiments. Results indicate that the electro-Fenton process yielded about 60-70% mineralization of ARK while the photoelectro-Fenton could mineralize AR14 more effectively (more than 94% total organic carbon (TOC) removal) even at low current densities assisted with UV irradiation after 6 h electrolysis. The mineralization current efficiency (MCE) of the PEF process increased with the increasing AR14 concentrations. In addition, the initial solution pH ranging from 1.49 to 6.72 had little influence on the TOC removal probably due to the formation of organic carboxylic acids which balanced the pH increase caused by the cathodic generation of hydrogen gas. The ACF cathode showed a long-term stability during multiple experimental runs for degradation of ARK indicating its good potential for practical application in treating refractory organic pollutants in aqueous solutions. (C) 2008 Elsevier B.V. All rights reserved.