Kisspeptin, a placental polypeptide secreted throughout pregnancy, is suggested to play a role at parturition. Here we evaluated whether its placental mRNA expression and maternal/fetal plasma levels change at term and preterm delivery, and its effect on oxytocin secretion from placental explants. Samples were collected from 40 women with singleton pregnancies who underwent elective cesarean section at term (TNL), term vaginal delivery (TD), and preterm vaginal delivery (PTD). Plasma Kisspeptin and oxytocin levels were assessed by ELISA; placental mRNA expression by Real-time quantitative RT-PCR analysis. Placental expression was significantly (P < 0.0001) higher in PTD than TNL and TD and significantly (P < 0.001) higher in TD than TNL. Maternal/fetal plasma concentrations did not differ among the groups, and maternal were significantly higher than fetal levels (P < 0.05). In placental explants increasing doses of kisspeptin did not modify oxytocin secretion. In conclusion, labor is associated with increased placental KiSS-1 expression without changes in maternal/fetal circulation.