Background: Various pain treatments have been administered to relieve patients suffering from postoperative pain. Among these, epidural or intravenous opiate administration is by far the most widly applied treatment in recent times. However it was our objective to device a more effective and safe means of postoperative analgesia. Methods: We studied 110 healthy pregnant women scheduled for delivery by elective cesarean section. EPI(epidural)-group is administered morphine 1.5 mg and 0.25% bupivacaine 8 ml as bolus dose, then, a mixture of morphine 6 mg and 0.125% bupivacaine 95 ml as continuous dose via epidural route. IV(intravenous)-group is administered nalbuphine 6~7 mg as bolus dose and nalbuphine 60~70 mg with 0.9% normal saline 90 ml as continuous dose via intravenous route, at the rate of 2 ml/hr for 2 days. We compared the analgesic efficacy and side effects of these two groups using VAS pain score and time duration of constant pain level. Results: VAS pain score was similar between the two groups, but pain duration was significantly shorter in EPI-group. Incidence of pruritus was significantly lower with the IV-group, of nausea and vomiting were similar for both groups, no respiratory depression for either groups. Conclusions: Although the EPI-group had better analgesic efficacy, the IV-group had lower incidence of side effects, and simplicity and safety methods of operation. Therefore, We propose further research and consideration of administering the kinds and doses of those medications prescribe to the IV group in conjunction with other drugs for safer and better efficacy of postoperative analgesia.