Decomposition of acetic acid, known as a non-degradable organic compound, was conducted for several advanced oxidation processes such as TiO2-UV-H2O2, Fe2+-H2O2-UV, UV-H2O2 and TiO2-UV system. Acetic acid was efficiency decomposed within 120 minutes of UV radiation under the initial concentration of 500 ppm. The initial chemical oxygen demands (CODcr) tended to increase as H2O2 was added in most reactions. However, the initial CODcr was not increased as H2O2 was consumed for the oxidation of iron salt in the photo-Fenton oxidation process. CODcr and concentration of acetic acid rapidly decreased as the mole ratio of hydrogen peroxide increased owing to rapid decomposition of the reactant at the beginning of reaction. All reactions show first order pseudo reaction rate. The CODcr removal rate and the decomposition efficiency of acetic acid were fastest in the UV-H2O2 process.