Herein, we report an enantioselective aziridination reaction using a planar chiral rhodium indenyl catalyst and unravel the origin of the enantioselectivity by DFT calculations. The reaction provides a wide range of enantioenriched aziridines and shows remarkable selectivity for unactivated olefins in the presence of activated olefin motifs. The mild reaction conditions and easy preparation of the catalyst represent additional features and contribute to the versatility of the reaction. Computational studies revealed that activation of hydroxylamine occurs prior to olefin engagement. Both nitrene and π-allyl complex formation are less favorable than the formation of amide intermediate. The amide intermediate undergoes an olefin insertion step, which is both enantio-and rate-determining step. The enantioselectivity arises from the difference in steric clash between olefin and amide intermediate, which favors the olefin bound intermediate forming (S)-aziridine. The fact that the simple planar chiral indenyl catalyst can induce such high levels of enantioselectivity in both the previously reported allylic amidation reaction, and this mechanistically distinct aziridination reaction suggests it is a versatile catalyst platform with significant potential for further development.