Modulation-frequency dependent photoacoustic (PA) spectroscopy was applied to gold-deposited titanium(IV) oxide powders in the presence of adsorbed methanol to detect the PA signal owing to phenomena occurring during photocatalytic reactions, e.g., release of reaction heat. Analysis of peak frequency of Helmholtz resonance provided qualitative information on changes in gas composition induced by photocatalytic reactions (oxidation or dehydrogenation of methanol), which depended on the presence or absence of oxygen. The PA signal attributable to heat of photocaralytic reaction was observed by canceling the effect of changes in gas composition using two kinds of modulated light as excitation and non-excitation for photocatalytic reaction. (C) 2007 Elsevier B.V. All rights reserved.