Molecular iodine was first utilized for direct oxidation of a-isophorone (a-IP) to ketoisophorone (KIP) with molecule oxygen at room temperature and the effects of amount of iodine,solvents and reaction time were investigated extensively.The optimized result shows that 70.2％ conversion of α-isophorone and 82.6％ selectivity of ketoisophorone are obtained with 15％ iodine (molar fraction) in acetonitrile under photoirradiation for 5 h.Moreover,the possible mechanism is proposed.