The investigation of in situ photoelectrocatalytic degradation of the methylene blue (MB) molecules merged into a nano-TiO2 modified film by electrochemical techniques is proposed. The methylene blue-Nafion-TiO2 (MB/Nf/TiO2) modified platinum electrode shows a reversible and faster electron-transfer efficiency in photoelectrocatalytic degradation reactions of surrounding compounds adsorbed on photocatalyst. Open-circuit potential (E-oc) of the MB/Nf/TiO2 electrode shows that the MB molecules have an assured effect with transferred photogenerated electrons on the Nf/TiO2 interface under UV illumination. A linear regression equation is obtained by the cyclic voltammetry peak current of the residual MB and the reaction time in the degradation process, in which MB undergoes demethylation and C = N bond breaking. (C) 2008 The Electrochemical Society.