BACKGROUND: Epidural and intravenous (IV) administration of opioids are commonly used for postoperative pain management. However, studies that compare the epidural and IV routes of opiate administration show conflicting results. The purpose of this study was to determine the superior route of analgesics by comparing the effect of epidural fentanyl-bupivacaine with IV morphine using patient-controlled analgesia (PCA) system in the management of posterior thoracic surgery pain. METHODS: Sixty patients undergoing elective thoracic surgery were randomly assigned to receive either Epiural-PCA (Epi-PCA, n=30) or IV-PCA (n=30) when postoperative pain first increased to 40/100 mm (by visual analogue scale; VAS). Epi-PCA group received epidural bolus of 0.1% bupivacaine 10 ml containing fentanyl 100 microgram and then followed by Epi-PCA with 0.1% bupivacaine 100 ml containing fentanyl 800 microgram (basal infusion 2 ml/hr, PCA dose 1 ml, lock-out interval 30 min), IV-PCA group received repeated IV boluses of 3 mg of morphine until postoperative pain decreased to 40/100 mm and then followed by a IV-PCA with morphine (basal infusion 0.005 mg/kg/hr, PCA dose 0.02 mg/kg, lock-out interval 8 min). Analgesic efficacy, degree of patient satisfaction and pain, analgesics consumptions, forced vital capacity (FVC), forced expired volume in one second (FEV1) and side effects were evaluated. RESULTS: There were no significant differences in analgesic efficacy and degree of patient satisfaction and pain in both group. But the PHS were significantly lower (p<.05), and FEV1 higher (p<.05) in Epi-PCA group, signifying better analgesia during movement (cough and deep breaths). CONCLUSIONS: We concluded that an epidural PCA with mixture of fentanyl and bupivacaine administration is superior to that of intravenous PCA with morphine in the management of pain after thoracic surgery.