Abstract: Objective：To investigate the role of RhoA/Rho Kinase pathway in the postpartum hemorrhage by uterine atony. Methods：Sixty term delivery women were selected and divided into 2 groups：30 in postpartum hemorrhage caused by uterine atony and 30 in control group. The levels of contraction of myometrium were detected by RM6240 biological experimental system；the fluorescence quantitative RT-PCR and Western Blot were applied to detect the expression of RhoA， ROCKⅠ，ROCKⅡin myometrium. Results：①The levels of myometrium contraction in study group were lower than that of control group（P＜0.01），when adding the Rho kinase inhibitor Y-27632 to strips，the levels of myometrium contraction in both group and control group were lower than untreated（P＜0.01）. ②The mRNA expression of RhoA，ROCKⅠ，ROCKⅡ in study group were lower than control group（P＜0.05，P＜0.01）. ③The protein expressions of RhoA，ROCKⅠ，ROCKⅡin study group were lower than control group（P＜0.05，P＜0.01）. ④Both groups，RhoA mRNA and protein levels in myometrium were positively related to the levels of ROCKⅠ，ROCKⅡmRNA and protein. ⑤Both groups，RhoA，ROCKⅠ，ROCKⅡmRNA and protein levels in myometrium were positively related to the levels of myometrium contraction. Conclusions：Decreased RhoA/Rho Kinase Pathway expression in myometrium may be involved in the pathogenesis of postpartum hemorrhage by uterine atony.

Key words: Myocytes, smooth muscle, Myometrium, Postpartum hemorrhage, Uterine inertia, rhoA GTP-binding protein