Background : Patient-controlled analgesia(PCA) is a safe and effective technique for providing postoperative pain relief. Studies that compare epidural vs intravenous routes of opiate administration show conflicting results. We designed a prospective, randomized, controlled study to evaluate the safety and efficacy of epidural(EPI-PCA) morphine-bupivacaine versus intravenous (IV-PCA) nalbuphine when administered with a PCA system. Methods : Forty healthy women were randomly assigned to receive an epidural bolus of morphine 3 mg and 0.5% bupivacaine 10 ml, followed by a EPI-PCA with 0.01% morphine and 0.143% bupivacane (basal infusion 1 ml/hr, bolus 1 ml, lock-out interval 30 min) or intravenous bolus of nalbuphine 0.1 mg/kg followed by a IV-PCA with nalbuphine(basal infusion 1 mg/hr, bolus 1 ml, lock-out interval 20 min) for pain relief after cesarean delivery. This study was conducted for 2 days after cesarean section to compare the analgesic efficacy, side effects, patient satisfaction either as EPI-PCA or as IV-PCA. Results : EPI-PCA group had significant lower visual analog pain scale(VAS) at immediate postoperative period, whereas no significant difference was observed when pain was assessed at other time sequence. Urinary retention and pruritus were more frequent with EPI-PCA group, although the incidence of other side effects were the same. Conclusions : Although EPI-PCA with morphine-bupivacaine was of significantly lower VAS at immediate postoperative period, IV-PCA with nalbuphine is a safe and effective alternative to EPI-PCA with morphine-bupivacaine for providing pain relief after cesarean delivery. Further studies about IV-PCA with nalbuphine are needed to control the immediate postoperative pain and to further improve effective pain management.