ObjectiveMatrix metalloproteinases (MMPs) are a family of endoproteases produced by various tissues and cells and play important roles in angiogenesis, tissue repair, immune response, and endometrial remodeling. However, the expression and function of MMPs in the pig endometrium during the estrous cycle and pregnancy have not been fully elucidated. Thus, we determined the expression, localization, and regulation ofMMP2,MMP8,MMP9,MMP12, andMMP13in the endometrium throughout the estrous cycle and at the maternal-conceptus interface during pregnancy in pigs.MethodsEndometrial tissues during the estrous cycle and pregnancy and conceptus and chorioallantoic tissues during pregnancy were obtained and the expression of MMPs was analyzed. The effects of steroid hormones and cytokines on the expression of MMPs were determined in endometrial explant cultures.ResultsExpression levels ofMMP12andMMP13changed during the estrous cycle, while expression ofMMP2,MMP9,MMP12, andMMP13changed during pregnancy. Expression ofMMP2,MMP8, andMMP13mRNAs was cell type-specific at the maternal-conceptus interface. Gelatin zymography showed that enzymatically active MMP2 was present in endometrial tissues. In endometrial explant cultures, estradiol-17β induced the expression ofMMP8andMMP12, progesterone decreased the expression ofMMP12, interleukin-1β increased the expression ofMMP2,MMP8,MMP9, andMMP13, and interferon-γ increased the expression ofMMP2.ConclusionThese results suggest that MMPs expressed in response to steroids and cytokines play an important role in the establishment and maintenance of pregnancy by regulating endometrial remodeling and processing bioactive molecules in pigs.