Abstract: The novel 13, 14-dihydro-15-keto prostaglandins E of the invention have remarkable preventive effects against ulcers. Further, the novel 13,14-dihydro-15-keto prostaglandins E of the invention have an advatage that they have none of side effects which prostaglandin E intrinsically has, or can remarakably reduce such effects of the prostaglandin E. Therefore, the novel 13, 14-dihydro-15-keto prostaglandins E of the invention are effective for animal and human use for treatment and prevention of ulcers, such as duodenal ulcer and gastric ulcer.