A process for preparing a .beta.-lactam halide compound represented by the formula (2) characterized by halogenating the allenyl group of an allenyl .beta.-lactam compound represented by the formula (1) with a cupric halide and a metal halide to obtain the .beta.-lactam halide compound ##STR1## wherein R.sup.1 is a hydrogen atom or amino or protected amino, R.sup.2 is a hydrogen atom, halogen atom, lower alkoxyl, lower acyl, or lower alkyl having a hydroxyl group or protected hydroxyl group as a substituent, R.sup.3 is a hydrogen atom or carboxylic acid protecting group, and R.sup.4 is a hydrocarbon group which may have a substituent, or the group --S--S(O)n-Ar, n being 0 to 2, Ar being aryl which may have a substituent ##STR2## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same as defined above, X and Y are each halogen atom.