The Oxidation of various substrates such as benzylic methylenes, sulfides, thiophosphates, and nitroalkane was carried out by peroxy intermediates in situ generated from organo halides and superoxide. The chemical reactivities of these peroxy intermediates were studied by chemical experiments and the radical species of these intermediates were confirmed by spin trapping studies. In connection with the metabolic oxidation of nucleosides and insecticides, biominic oxidation of various substrates such as inosine, parathion, thiouridine, and aldrin by peroxy intermediates was examined. A new oxidizing agent of iodosobenzene and benzeneseleninic acid as a catalyst has been developed and used for the stepwise and chemoselective oxidation of sulfides. Asymmetric oxidation of sulfides and asymmetric $\alpha$ hydroxylation of carbonyl compounds were studied using new chiral oxidants.