BACKGROUND: Continuous epidural morphine infusion is a good and popular method to control postoperative pain. But intravenous morphine infusion after general anesthesia can avoid anxiety during operation and also control postoperative pain. We compared analgesia and side effects between continuous epidural infusion and continuous intravenous infusion of morphine sulfate to control of postoperative pain after cesarean section. METHODS: Forty women who received cesarean section were randomly divided into epidural and IV groups. Morphine 0.08 mg/kg was administered intravenously as an initial loading dosage for both groups. Morphine 0.08 mg/kg for epidural group or morphine 0.8 mg/kg for IV group was diluted into 96ml of normal saline. A mixture was injected into Two-day Infusor which is continuously infused 2 ml/hr. The patients received morphine solution into epidural or intravenous route with Two-day Infusor according to their allocated group. The assessments for pain score with VAS, VRS, patient's satisfaction score and side effects were made at recovery room, 0.5, 3, 12, 24, 36, 48 and 60 hours after operation. RESULTS: The VAS in IV group was significantly higher than that in epidural group at 3, 12, 24 and 36 hours after the operation (P<0.05). The VRS in IV group was significantly higher than in epidural group at recovery room and 3 hours of postoperative period (p<0.05). The frequency of pruritus, nausea, vomiting, back pain and urinary retention were less in IV group than in epidural group. The patient's satisfaction scores were similar in both groups. CONCLUSIONS: The management of postoperative pain in epidural group was more effective than the continuous intravenous morphine infusion. But the incidence of complications was more frequent in the epidural group while patient's satisfaction scores were similar in both groups. Therefore, the continuous intravenous morphine infusion can be used effectively as a postoperative pain management.