A combination of Chloramine-M (CH3SO2NClNa), benzaldehyde, and benzyltriethylammonium chloride (BTEAC) was found to epoxidize a wide range of olefins. While epoxidation of trans-olefins provided exclusively trans-epoxides, cis-olefins (cis-stilbene, cis-beta-methylstyrene, and 4-cis-octene) gave trans-epoxides as major products. Good to excellent diastereoselectivities were obtained for epoxidation of two substituted cyclohexenes. Chloramine-T was found to give a slower reaction than Chloramine-M, cis-N-Sulfonyloxaziridine D is proposed to be the epoxidizing agent in this novel epoxidation reaction on the basis of the mechanistic studies.