Immobilized vitamin B-12 within nanoreactors of Al-MCM-41 (Vit.B-12/Al-MCM-41) was used as catalyst in the photooxidation of cyclohexene with molecular oxygen in CH3CN using medium pressure mercury lamp at room temperature. It was found that 99% of cyclohexene was converted to 2-cyclohexene-1-one (70%), 2-cyclohexene-1-ol (15%) and cyclohexene oxide (15%). Details of reaction are discussed.