Introduction : Continous thoracic epirdural infusion of local anesthetics can provide postoperative analgesia following thoracotomy and upper abdominal surgery. Bupivacaine in commonly used for its selective sensory blockade.Objective : In this prospective study, we compared the efficacy and safety of continuous thoracic epidural infusion with bupivacaine in 3 doses.Methods : Sixty patients undergoing thoracic or upper abdominal surgery were equally randomised into 3 groups ; 3.75 mg/hr of bupivacaine in group 3.1, 7.5 mg/hr in group 2 and 15 mg/hr in group 3. The infusion rate was 6 ml/hr for 48 hours postoperatively. The efficacy was evaluated by total milligrams of supplementary morphine via intravenous PCA.Results : At the 24th hour postoperatively, the total dosages of morphine were 35.85, 29.65 and 22.32 mg in group 1, 2 and 3 respectively. The total morphine of group 3 was signigicantly less than group 1 but was not significantly different from group 2. The higher average age in group 2 seemed to lessen the local anesthetic requirement and no statistical ddifference was detected between group 2 and 3. But after 24 hours postoperatively, there was no statistical difference for the total dose of morphine as 20.25, 17.80 and 15.68 mg in group 1, 2 and 3 respectively. There was no statistical difference for severity of pain at rest and during exercise among the 3 groups when they were evaluated by numeric rating scale 0-10. Hypotension was found for 1 case in group 2,which responded to colloid replacement and 1 case in group 3, which required multiple doses of vasopressor and crystalloid.Conclusion : For the first 24 hours postoperatively, infusion of bupivacaine 15 mg/hr via thoracic epidural catheter seemed to be the most effective dose for pain relief in the patients undergoing thoracic or upper abdominal surgery. Lower dose would be considered in elderly patients. However, after 24 hours the efficacy of higher dose (15 mg/hr) was not better than 3.75 mg/hr. Circulatory monitoring was required throughout the period of bupivacaine administration.