V2O5/Al2O3 exhibits the high selectivity to partial oxidation compounds (cyclohexanol and cyclohexanone) as compared with TiO2 in the photo-oxidation of cyclohexane in the liquid phase. This reaction is an environmentally friendly reaction since it proceeds at ambient temperature and atmospheric pressure without a solvent. The features of the reaction are a high selectivity to partial oxidation products and a reasonable ketone/alcohol ratio (K/A ratio). However, by elongation of the photoirradiation time, cyclohexyl hexanoate as a by-product was generated and the K/A ratio decreased gradually. Retention of the high O-2 concentration in the gas phase and irradiation of light lambda > 330 nm are keys to the selective formation of the partial oxidation compounds with a reasonable K/A ratio in the photo-oxidation of cyclohexane over V2O5/Al2O3. In the present study, a selectivity of 87% to the partial oxidation compounds was achieved with the K/A ratio of 3.8. (C) 2003 Elsevier B.V. All rights reserved.