Objective To investigate the influence of nilestriol on endometria of ovariectomized rats. Methods Thirty-six female 7-month old Sprague-Dawley rats were divided randomly into sham-operation group(12 rats) and model group(24 rats).Bilateral ovariectomy was performed on the rats of model group.The rats of sham-operation group were only sham operated.Two months after operation the model group was divided randomly into two subgroups: model group and nilestriol group.Nilestriol group was treated with nilestriol;model group and sham-operation group received saline.After two months of the treatment all rats were killed and the endometria were removed and processed for histopathological examination.Result In model group(8 rats) the endometria were of proliferative phase or atrophy phase.In sham-operation group the ecndometria were of proliferative phase(5 rats) and secretory phase(3 rats).In nilestriol group all of the endometria were of secretory phase(8 rats).Conclusion Nilestriol can induce a secretory phase endometria in ovariectomized rats.Because those results are in apparent contrary to the current endocrinology theory and are different from the reports of previous animal experiments,we decided to make this report and believe it deserves further studies.