The purpose of the present study was to investigate the effect of IFN- on prostaglandin synthesis, cyclooxygenase-2 (COX-2) gene expression in vitro and concentration of progesterone (P4) in endometrial cells. Epithelial and stromal cells cultured in vitro were isolated from bovine endometrium and stimulated with increasing doses of IFN- (0, 0.02, 0.2 and 2 ug/ml). Human chorionic gonadotropin (hCG, 1.5 IU/ml) was used as a positive control. Prostaglandin and levels in the culture media were analyzed by enzyme immunoassays and total RNA was extracted from the cells for RT-PCR. P4 concentrations of blood samples were assayed by chemiluminescent immuno assays system. In epithelial cells, COX-2 gene expression was increased in the presence of IFN- (p<0.05), but it was not significantly different in all groups of stromal cells except for 2 ug/ml IFN- group (p<0.05). Although IFN- did not affect and production in epithelial cells, it decreased and production significantly in stromal cells (p<0.05). In vivo experiment, blood concentration of P4 was significantly increased after addition of IFN- (1 ug/ml). The results indicate that PG production was mediated by COX-2 expression in stromal cells but it was not affected in epithelial cells and this suggest that treatment of IFN- could improve the implantation environment of uterine by maintenance of high P4 concentration.