PURPOSE: To provide a carba(dethia)cephalosporin antibiotic useful as antibacterial agent effective against both gram-negative and gram-positive bacteria.

CONSTITUTION: A compound of formula I [X is amino, halo, etc.; R3 is H, 1-4C alkoxy, etc.; R1 is an acyl of formula II (R2 is H, cyano, etc.)] or its salt, e.g. 7β-[(2-aminothiazol-4-yl)-Z-hydroxyiminoacetylamino]-1-carba(1-dethia)-3-[2-(4- nitro-3-methylimidazol-2-yl)thiazol-4-yl]-3-cephem-4-carboxylic acid. The compound is obtained by reacting a compound of formula III with a compound of formula, IV (X is methyl or n-butyl), reacting the resultant product with bromine/carbon tetrachloride, subjecting the resultant product successively to acylation, substitution with a base and acidically catalytic hydrogenolysis to form a novel intermediate of formula V, reacting the product with a compound of formula VI and subjecting the resultant product successively to reesterification and deprotection.