ABSTRACT. The morphology of the uterine wall in the postpartum Chinese hamster (Cricetulus griceus) was studied with particular reference to the changes in the arterioles in the mesometrial endometrium. At day 0 postpartum, the endometrial arterioles were characterized by the appearance of trophoblastic giant cells plugging ruptured arterioles. On days 1 to 3 postpartum, the giant cells were replaced by epitheloid cells. On days 4 to 5 postpartum, the epitheloid cell mass was invaded by fibroblasts to occlude the arterial lumens. On days 6 to 7 postpartum, endometrial regeneration was completed. The giant cell might play a role in hemostasis immediately after parturition. -KEY WORDS: Chinese hamster, endometrial arteriole, postpartum.