A practical catalytic method to oxidize α-ionone with molecular oxygen using N-hydroxyphthalimide(NHPI) combined with acetylaeetone cobatt(Ⅱ) (Co(acac)2) was developed, and the probable catalytic mechanism was proposed. The influences of the reaction conditions on conversion of α-ionone and the selectivity of the major product (5-keto-ct-ionone) were investigated, and the technical parameters for 5-keto-α-ionone were optimized. The results show that the primary product is 5-keto-α-ionone, and by-products include epoxy-α-ionone, as well as rearrangement products 4-keto-β-ionone and epoxy-β-ionone, which are characterized by infrared spectra, proton nuclear magnetic resonance spectra, mass spectra and elemental analysis. The selectivity of 5-keto-α-ionone and the conversion of α-ionone are 55.0% and 97.0%, respectively, when 30%(molar fraction) NHPI, 1.0%(molar fraction) Co(acac)2 and no solvent are employed under O2 pressure of 1.0 MPa and the reaction temperature of 65℃ for 11 h. The procedure shows good reproducibility in the parallel experiments.