The present study was conducted to identify the morphological characteristics of the placental barrier and localization of estrogen receptors α in the cow and buffalo placentas. Placentomes were collected from 3 pregnant cows and 3 pregnant buffaloes at the 5^th and 6^th months of gestation respectively. The placentomes were fixed by using 10% neutral buffered formalin for immunohistochimestry and were post fixed in 3% glutaraldehyde for light microscopy. Indirect immunoperoxidase staining methods using monoclonal antibody against bovine ERα as primary antibody was applied. The morphometric data were obtained by using Q500 MC Image processing and analysis program. Histological examination revealed that there is a great similarity in the structure of the placental barrier of cows and buffaloes, whereas typical six slayers of tissue were seen separating the fetal blood from the maternal one. These layers were maternal endothelium, thin layer of maternal connective tissue, maternal uterine epithelial cells, fetal trophoblast cells, fetal connective tissue and fetal endothelium. Nuclear immunoreactivities occurred mainly in the maternal crypt epithelium and maternal connective tissue cells. In about 1000 maternal uterine cryptal cells, 87.6% were positive cells for ERα in the cow placenta and about 67.8% were positive cells in the buffalo placenta. The present study concluded that although there is a great similarity in the structure of the placental barrier and expression of ERα in the placentas of cows and buffaloes interbreeding between the two species is impossible due to the different number of chromosomes set. The placenta of cows seems to be less responsive to estrogen in comparison to that of buffaloes.