This study was conducted to evaluate the effect of a photocatalysis/oxidant system for the treatment of humic acid and heavy metals in aqueous solutions. Hydrogen peroxide, ozone and potassium peroxodisulfate were tested as oxidants. The effect of the oxidant concentration was conducted with a pH of 7, a UV intensity of 64 W and a TiO2 dosage of 0.3 g/L. The addition of oxidants over the amounts of H2O2 50 mg/L, O3 20 g/m3 and K2S2O8 50 mg/L inhibits the system efficiency. The negative effect of the high concentration of oxidants likely results from OH radical quenching caused by the excess oxidant. Therefore, the optimal dosages for the oxidants such as a hydrogen peroxide, ozone and potassium peroxodisulfate were found to be 50 mg/L, 20 g/m3 and 50 mg/L, respectively. The addition of an oxidant in the UV/TiO2 system enhanced the degradation efficiency of humic acid and heavy metals compared to no addition of an oxidant. The degradation efficiency of humic acid and heavy metals was much greater for the UV/TiO2/H2O2 system.