The present invention relates to a new aziridine derivative that is represented herein by general chemical formulae (Ia) or (Ib), and to their preparation method. In the said chemical formulae, R₂ and R₃ can be the same or different, and they are hydrogen, low-quality alkyl or cycloalkyl respectively; R₄ can be selected among hydrogen, alkyl, aryl, or amino protective group; and amino protective group is, for example, (Ph)₃C, and FMOC(9-fluorenylmethyloxycarbonyl), alkoxycarbonyl, aryloxycarbonyl, aralkyloxycarbonyl and R₅CO, R₅SO₂ where R₅ is alkyl, aryl or aralkyl.