This review article summarizes the electron transfer reactions of piperidine aminoxyl radicals. Electrochemical studies revealed the single electron transfer nature of piperidine aminoxyl radicals. In solution, piperidine aminoxyl radicals serve as single electron transfer oxidation reagent to react with various biologically interesting molecules such as glutathione, cysteine, ascorbic acid, and amines. The reaction product distribution, reaction kinetics, intermediates, and the reaction features in biological mimic environments including micelles and cyclodextrins were investigated. Oxoammonium salts, the one-electron transfer oxidation products of piperidine aminoxyl radicals, are agents of organic synthesis to selectively generate ketones or di-ketones from alcohols or ketones bearing α-methylene group under mild conditions. The new reactions of oxoammonium salts with aromatic amines, phenols, heterocycles including phenothiazines, papaverine, and bilirubin are also illustrated. This review article summarizes the electron transfer reactions of piperidine aminoxyl radicals. Piperazine aminoxyl radical serve as single electron transfer oxidation react to react with various biologically interesting molecules such as glutathione, cysteine, ascorbic acid, and amines. The reaction product distribution, reaction kinetics, intermediates, and the reaction features in biological mimic environments including micelles and cyclodextrins were investigated. Oxoammonium salts, the one-electron transfer oxidation products of piperidine aminoxyl radicals, are agents of organic synthesis to selectively generate ketones or di-ketones from alcohols or ketones bearing alpha-methylene group under mild conditions. The new reactions of oxoammonium salts with aromatic amines, phenols, heterocycles including phenothiazines, papaverine, and bilirubin are also illustrated.