Abstract: Thiourea derivatives represented by the formula (I) ##STR1## wherein R.sub.1 and R.sub.2 are the same or different and each represents a lower alkyl group, or R.sub.1 or R.sub.2 taken together represent a group having the formula --(CH.sub.2).sub.m --in which m is 4 or 5, R.sub.3 represents a lower alkyl group or a cycloalkyl group or a group having the formula--(CH.sub.2).sub.l --R.sub.4 in which R.sub.4 is a phenyl, naphthyl, pyridyl, furyl or thienyl group optionally having 1-3 substituents selected from the group consisting of lower alkyl, lower alkoxy, phenoxy, lower alkylthio, hydroxy, halogen, nitro, cyano and trifluoromethyl, and l represents an integer of 0 to 2 and n represents an integer of 1 to 5 or a physiologically acceptable salt thereof.The compounds of the invention are useful as a therapeutic agent for peptic ulcers which is also effective on prevention of the recurrence after discontinuation of the administration due to the antimicrobial activity against Helicobacter pyroli.