Photocatalytic degradation of single and binary mixtures of o-cresol and 4-chlorophenol (4-CP) over TiO2 suspensions under UV irradiation was studied and the mixture effect was discussed. The effects of operating parameters such as initial reactant concentration (0.16-1.04 mM), solution pH (4.50-9.35), and UV light intensity (20-100 W) on the degradation were investigated. It was shown that the degradation of single or binary mixtures of reactants in aqueous solutions could be described by the pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. When the second reactant was in excess, the degradation rates of o-cresol and 4-CP in binary mixture system were slower than those in single systems. At a fixed o-cresol concentration of 0.45 mM, for example, the apparent first-order rate constant kapp for o-cresol degradation was 0.323, 0.275, and 0.220 h−1 when 0.15, 0.30, and 0.45 mM of 4-CP was present, respectively.