Derivatives of cyclic guanidine are disclosed, which are represented by the following formula:A--S--Rwherein A is ##STR1## R.sub.1 represent a lower alkyl or substituted phenyl or unsubstituted phenyl group; R.sub.2 is a lower alkyl; R.sub.3 is H or a lower alkyl; R is lower alkyl, alkenyl, alkynyl, alkanoyl, alkenoyl, dialkylaminoalkyl, cyanoalkyl, alkoxycarbonylalkyl, carboxylalkenyl, alkoxycarbonyl, alkoxyalkylcarbonyl, dialkylaminocarbonyl, dialkylaminothiocarbonyl, phenoxyalkylcarbonyl, piperidinoalkyl, pyridine carbonyl, substituted or unsubstituted benzoyl, or substituted or unsubstituted benzyl group. The compounds of the present invention are useful as anti-ulcerative agents.