Abstract: The photodegradation of the three cyclic hydrocarbons in petroleum, ethyl benzene， tetrohydronaphthalene anddecahydronaphthalene was s tudied. A high pressure mercury lamp and the sunlight were respectively used as the light sources. The results of the experiments showed that the three componen ts all could be photodegraded under the high pressure mercury lamp, but not unde r the sunlight. When there is Fenton reagent (Fe^２＋+ H_２ Ｏ₂) or particles of TiO₂ or ZnO in the reaction system, the three cyclic hydrocarbons could all be degraded under either the high pressure mercury lamp or the sunlight. The sequence of the rates of the photodeg radation wastetrohydronaphthalene＞decahydronaphthalene＞ethyl benzene. The opt ium photodegradation conditions were selected.

Key words: hydrocarbons in petroleum, photodegradation, water