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a b s t r a c tIn this research, methylene blue (MB) was use as a pollutant to investigate the capability of dye degradation of photocatalytic (UV/TiO 2 ) and photoelectrocatalytic (UV/TiO 2 /bias) reaction, and also the condition for UV/TiO 2 /bias process was optimized. The photocatalytic process with bias potential was conducted in aqueous supporting electrolyte and with a proton exchange membrane (Nafion 117). Comparing with the general use of aqueous electrolyte (e.g. NaSO 4 , KCl, or NaCl) in photoelectrocatalytic process, this study was focused on the application of proton exchange membrane as a solid electrolyte for the photoelectrocatalytic decomposition of MB. The degradation of MB was experimentally studied by a varied reaction condition (i.e. solution pH value, UV light intensity, initial dye concentration, gas introduction, supporting electrolyte concentration, and bias potential). Degradation of MB was enhanced in UV/TiO 2 /bias process as compared to that carried out in UV/TiO 2 process, especially as the Nafion membrane was applied (UV/TiO 2 /Nafion process). The photodegradation rates could also be boosted by increasing the concentration of supporting electrolyte, concentration of dissolving oxygen and UV light intensity. In UV/TiO 2 /Nafion process, the rate constants of MB degradation increased as increasing bias potential to a certain level, and then it leveled off. The suitable bias potentials for experiments conducted at pH 5.3 and 7.0 were found to be 0.5 and 0.6 V, respectively.