Objective: To study the ED50 and ED95 of intrathecal ropivacaine for severe preeclamptic patients undergoing cesarean section. Method: The study population comprised 300 severe preeclamptic patients undergoing elective cesarean section. They were randomized, double-blinded into 6 equal groups who received 7.5mg,10mg,12.5mg,15mg and 17.5mg. Additional epidural analgesia was an epidural injection of 5ml of 0.75% ropivacaine if the spinal anesthesia was failure. The use of ropivacaine and phenylephrine and the patients’ satisfaction was recorded. Intraoperative compIications and the newborns’ Apgar score were documented． Results: ED50 and ED95 of intrathecal ropivacaine for successful spinal anesthesia were 9.3 mg (95% confidence interval [CI]: 8.6-9.9mg) and 14.9mg (95% CI: 13.7-16.9mg) respectively. The sensory block was significantly different among groups 10 minutes after intrathecal injection(P < 0.05). The incidence of hypotension in Group 17.5 mg and Group 15 mg was higher than that in Group 7.5 mg and Group10 mg (P < 0.05). The use of phenyIephrine in groups 15mg and 17.5mg was higher than that in other two groups(P < 0.05). The use of ropivacaine in group 7.5mg and 10mg was higher than that in other groups(P < 0.05). There was no significant difference in patients’ satisfaction, the Apgar score of newborns (P>O．05)among four groups． Conclusion: Our study showed that the ED50 and ED95 of intrathecal ropivacaine for severely preeclamptic patients undergoing elective cesarean delivery were 9.3 mg and 14.9 mg, respectively.