Prostaglandins (PGs) are produced by the intrauterine tissues of pregnancy and play important role in all of the physiological processes of parturition. PGs are synthesized from arachidonic acid by the action of cyclooxygenase (COX). Nitric oxide (NO) is a potent smooth muscle relaxant and is considered to be an important local mediator that suppresses uterine contractility. There may be an interaction between the NO and PG pathways in regulating the nitric oxide synthase (NOS) and COX expression and this interaction may play a critical role in the control of cervical ripening and parturition. The purpose of this study is to examine the expression of cyclooxygenase-2 (COX-2), inducible NOS (iNOS) and endothelial NOS (eNOS) mRNA levels during gestation, parturition, and postpartum in pregnant rat uterus. Forty-two pregnant Sprague Dawley rats were randomly divided into 7 groups. Both uterine horns were removed and the pups and placentas were discarded. Complementary DNA (cDNA) was synthesized after isolation of total RNA from the tissues. The relative expression of iNOS, eNOS and COX-2 genes were measured by quantitative real-time polymerase chain reaction (QRT-PCR). The mRNA level of iNOS was increased during gestation; highest level in parturition and then it decreased at postpartum. The eNOS mRNA level was generally low during gestation in all groups and was significantly increased at postpartum. The COX-2 mRNA levels decreased as the pregnancy progressed to term with the highest level occurring on day 21 and the lovest levels during the postpartum period. In conclusion, there may be an interaction between the NO and PG pathways in cervical ripening and parturition. These results may show that mRNA levels of eNOS, iNOS and COX-2 genes may be effective cervical ripening during pregnancy and parturition.