3-Oxo-2-azabicyclohexane derivatives represented by the general formula: ##STR1## wherein R.sub.1 represents an optically active menthoxy group or an optically active 1-phenylethoxy group when R.sub.2 and R.sub.3 are combined to form a bond; when R.sub.3 is a hydrogen atom, R.sub.1 and R.sub.2 are combined to form an oxo group or, R.sub.2 is a hydrogen atom and R.sub.1 is a hydroxy group or a lower alkanoyloxy group. The 3-oxo-2-azabicyclohexane derivatives are novel compounds useful as intermediates for antibacterial agents.