It was found that N-{2-(2-thienyl)ethyl}succinimide (1) and N-{2-(2-thienyl)ethyl}glutarimide (2) had potent antiulcer activities. In order to obtain more excellent antiulcer agents, two kinds of cyclic carbamate derivatives (3, 4) were prepared by various methods and tested for antiulcer activities. As a result, 2-oxazolidinone derivatives (3a-d, f, q, r, t) and tetrahydro-2H-1, 3-oxazin-2-one derivatives (4a, c, e, h) showed potent antiulcer activities. As the most preferred compound, 3-(2-thienylmethyl) tetrahydro-2H-1, 3-oxazin-2-one (4a) was selected.