In the presence of an iridium compound, an imine of the following formula (1): ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are each, identical to or different from one another, a hydrogen atom or a non-reactive organic group, where R.sup.1 and R.sup.2 may be combined to form a ring together with the adjacent carbon atom, is reacted with a diazoacetic acid derivative of the following formula (2): wherein R.sup.4 is a cyano group, an alkoxycarbonyl group, a carbamoyl group or the like, to yield an aziridine compound of the following formula (5): ##STR2## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 have the same meanings as defined above. The process can easily and efficiently produce aziridine compounds.
