The mechanism and kinetics of synergetic effect in TiO2/O3/UV process on H-acid degradation were investigated. The experimental results showed that H-acid removal rate of TiO2/O3/UV process was the highest among TiO2/UV, O3/UV and TiO2/O3/UV processes. The investigation of reactions with suitable active species scavengers confirmed that H-acid was mainly oxidised by ozone and holes on TiO2 in the TiO2/O3/UV process. The recombination between holes and electrons in TiO2 reduced in the presence of ozone, as indicated by fluorescence emission spectra. Moreover, the intermediates generated during H-acid oxidation in various processes were analysed by LC/MSD trap. It is proposed that H-acid was oxidised to polyhydroxy aromatics, benzene carboxylic acids and quinoids in the first step. Then, saturated aliphatics carboxylic acids were formed and mineralised to inorganic compounds through the Photo-Kolbe reaction. Finally, a kinetic study on TiO2/UV, O3/UV and TiO2/O3/UV processes was conducted and it was confirmed that both ozonation and photocatalytic activity were improved in TiO2/O3/UV process because of the synergetic effect.