4-Thioquinazoline derivatives of formula (I) are provided. ##STR1## wherein R.sup.1 is a C.sub.1 -C.sub.6 alkylamino group, a phenyl group, a substituted phenyl group or a 5- or 6-membered heterocyclic group containing one or two N, O or S as a hetero atom or atoms, said heterocyclic group optionally being substituted or fused with a benzene ring; n is 1 or 2; or R.sup.2 is a hydrogen atom or a C.sub.1 -C.sub.6 alkyl group, and pharmaceutically acceptable acid addition salts thereof. They are useful as antiulcer agents.