Decorin (DCN) is a member of small leucine-rich proteoglycans which are ubiquitous components of the extracellular matrix. It regulates many physiological processes, such as matrix formation, collagen fibrillogenesis, angiogenesis, cancer growth, and cardiovascular diseases. It has been shown that DCN is expressed in the uterus during pregnancy and modulates implantation and decidualization for the establishment and maintenance of pregnancy in mice and humans. Expression of DCN in the uterine endometrium during pregnancy has not been investigated in pigs. Thus, this study investigated expression of DCN in the uterine endometrium during the estrous cycle and pregnancy in pigs. Uterine endometrial tissues were from day (D) 12 and 15 of the estrous cycle and D12, D15, D30, D60, D90, and D114 of pregnancy. Northern blot and real-time RT-PCR analyses showed that expression of DCN mRNA was detected throughout the estrous cycle and pregnancy with the highest levels during mid pregnancy. In situ hybridization analysis showed that DCN mRNA was localized to both luminal and glandular epithelia during the estrous cycle and pregnancy and also to chorionic membrane during mid pregnancy in pigs. To determine whether endometrial expression of DCN was affected by the somatic cell nuclear transfer (SCNT) procedure, DCN mRNA levels in the uterine endometrium from gilts with SCNT embryos on D30 of pregnancy were compared with those from gilts with normal embryos using real-time RT-PCR analysis. The result showed that DCN mRNA levels in the uterine endometrium were not significantly different between gilts with normal embryos and SCNT embryos. These results suggest that DCN may play an important role for endometrial tissue remodeling during mid pregnancy, and DCN expression is not affected by the SCNT procedure at the early stage of pregnancy in pigs.