[en] Photocatalytic activity of graft and supported vanadium oxide catalysts in the reaction of isobutylene oxidation, taking place under conventional conditions with the formation of incomplete oxidation product, is detected. It is ascertained, that supported vanadium catalysts have a higher specific and atomic photocatalytic activity, as compared with grafted ones. It is shown, that in the process of UV irradiation in the reaction medium active centres, which can conduct the reaction in obscure conditions, are formed