Teratogenic effects of 6,11-dihydro-11-oxodibenz[b,e]oxepin-3-acetic acid (oxepinac) were examined in mice and rabbits. Oxepinac was orally given to pregnant animals during the organogenesis period at 3, 30 and 90 mg/kg/day for mice, and at 3, 10 and 20 mg/kg/day for rabbits. It can be concluded that oxepinac has no teratogenic effect on fetuses in mice and rabbits. In addition, the medication of oxepinac to pregnant mice does not adversely affect the postnatal development of their pups.