The decomposition of catechol (o-hydrophenol) and resorcinol (m-hydrophenol) in aqueous solution by 254-nm UV direct photolysis and the UV-hydrogen peroxide (H2O2) process under various solution pH values was studied. The light absorbance and photolytic properties of catechol and resorcinol were found to be highly dependent on solution pH and can be adequately described with a three-species distribution model. For the UV-H2O2 process, the individual contribution to the decomposition of pollutants by direct photolysis and indirect hydroxyl radical destruction was differentiated by studying the linear addition of UV light absorbance of various reactant species. The contribution to the decomposition of the two hydrophenols by hydroxyl radical destruction was more than 95% in acidic and neural solutions for treatment with the UV-H2O2 process.