Objective:To explore the relationship between endogenous hydrogen sulfide(H2S)of the blood plasma and the contraction of myometrium. Methods:The sixty cord plasma samples were collected and divided into two groups according to the delivery has not launched the contractions. The concentration of H2S was assayed by sensitive sulphur electrode. The expressions of cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE) in placenta were measured by using immunohistochemistry. Results:H2S contents in the group which mothers did not start uterine contraction were higher than that mother started uterine contraction(P=0.01); The expressions of CSE were detected in cytoplasm of placental villi trophoblast cells and at higher levels in the group with mothers did not start uterine contraction. The expressions of CBS had not seen in both two groups. Conclusion:Cytoplasm of placental villi tropho- blast cells are included CSE and no CBS. The production of H2S in cord plasma is regulated by trophoblast cells. H2S content in cord placenta is related to initiation of parturition.