The pH-response drift of thermally grown oxide film on titanium electrode was investigated through Devanathen hydrogen permeation tests and open-circuit potential measurements. Thermostatic measurements using heat-treated titanium electrodes were conducted in solutions with pH being changed stepwise from pH 4 to pH 10. A numerical simulation of the pH-response drift based on a diffusion-controlled model was made using experimental values of hydrogen diffusion coefficient and oxide film concentrations as parameters. Results of the study showed that there was a relative lower pH-response drift in titanium electrodes heat-treated at 400-700degreesC for 10 min. Combined Auger electron spectroscopy and scanning electron microscopy (SEM) revealed the formation of a dense oxygen-rich film on these titanium electrodes. The retardation effect of this film is believed to be responsible for the low pH-response drift in such heat-treated electrodes. (C) 2003 The Electrochemical Society.