Abstract: 2-Azetidione derivatives represented by the following formula ##STR1## wherein X is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a hydroxyl group or a cyano group, l is 1 or 2, R.sup.1 is a lower alkyl group, a cycloalkyl group, a 1-naphthylmethyl group, an optionally substituted phenethyl group, an optionally substituted phenyl group, an optionally substituted benzyl group or a bis(alkoxycarbonyl)ethyl group, and R.sup.2 is a lower alkyl group, a lower alkoxy group, an amino group, an adamantyl group, a lower alkoxycarbonylmethyl group or an optionally substituted phenyl group, are disclosed. These compounds are useful as blood platelet aggregation inhibiting agents.