[reaction: see text] A simple procedure to obtain N-alkylsulfonyl- and N-arylsulfonyloxaziridines from the corresponding N-sulfinylimines involving a one-pot, two-step oxidation process with m-CPBA (1 equiv) and m-CPBA/KOH (1.1 equiv) is reported. The method is applicable to N-sulfinylimines derived from aldehydes (aliphatic and aromatic) and ketones (dialkyl and aryl alkyl) and preserves C=C-conjugated double bonds. Almost quantitative yields, very mild conditions (usually less than 5 min at room temperature), and easy purification by filtration are the main features of this new procedure, which can be performed at a gram scale.