This work elucidates the photodegradation of toluic acid isomers by UV/TiO2. Effects of the toluic acid isomers, pH and form of TiO2 on photodegradation are identified. The rate of photodegradation of toluic acid isomers in UV/TiO2 obey the sequence p > o > m. Additionally, the reaction rates under acidic conditions exceed those under neutral and alkaline conditions.