PURPOSE: To obtain a novel compound useful as an antibacterial agent exhibiting excellent activity especially on microorganisms of the genus Helicobacter and useful also as an antiulcer agent.

CONSTITUTION: A compound of the formula A-(CH2)m-X-(CH2)n-B (A is imidazol-1-yl or condensed imidazole ring group; X is 0 or S; B is heterocyclic group; (m) and (n) are 0-4), e.g. 1-(benzoxazol-2-yl) thioethyl-2-methyl-5- nitroimidazole. The compound can be produced by reacting a compound of the formula A-(CH2)m-Z (Z is reactive group) with a compound of the formula H-X-(CH2)n-B in a solvent (e.g. dichloromethane) optionally in the presence of a base (e.g sodium hydride) at -50 to +100°C. It is useful for the treatment of duodenal ulcer, gastric ulcer, chronic gastritis, stress ulcer, etc., caused by microorganisms of the genus Helicobacter, free from side action and having high stability and low toxicity.