Wet oxidation of 100 ppm aqueous solution of o-chlorophenol was performed in a batch reactor at 373, 413 and 433 K under 0.1 MPa oxygen pressure. The effects of an alkaline reagent (NaOH) and a catalyst(3% Ru/TiO2) on the decomposition of o-chlorophenol were investigated. The reaction time needed to attain 100% decomposition of o-chlorophenol at lower temperature was reduced by the addition of the alkaline reagent or Ru/TiO2 catalyst. The alkaline reagent played an important role in dechlorination of o-chlorophenol, resulting in the formation of organic acids (acetic and formic acids), and the generation of chlorine ion (HCl) through catechol as intermediate, but the complete decomposition of o-chlorophenol to inorganic compounds was not achieved. With the Ru/TiO2 catalyst, on the other hand, the main final products were inorganic compounds and chlorine ion, formed via p-chlorohydroquinone and organic acids as intermediates.