Intensity-modulated photocurrent spectroscopy (IMPS) was applied to studying the mechanism of photoelectrochemical decomposition of a model organic compound, ethanol, on a TiO2 anatase photoelectrode in aqueous solution. The frequency spectra of the intensity-modulated photocurrents observed on the TiO2 photoelectrode at low band bending were drastically changed in the presence of alcohol. Without the alcohol, the frequency dependence of the modulated photocurrents were similar to those reported previously for TiO2 electrodes and were typical for the case of surface recombination occurring on surface states, while upon addition of alcohol the photocurrent frequency dependence was no longer observed. This fact suggests that alcohol suppresses the recombination processes at the surface of the TiO2 photoelectrode. Possible mechanisms for this phenomenon are discussed. The results demonstrate that IMPS is a powerful tool for studying the mechanism of photocatalytic decomposition of organic pollutants on semiconductor electrodes.