Objective : To assess the epuivalence of analygesic effect between 0.0625% bupivacaine plus fentanyl 3 ug/ml and 0.15% ropivacaine delivered by patient-controlled epidural analgesia (PCEA) for 48 hours after unilateral total knee replacement (TKR) surgery. Design : Randomized double blind controlled trial Setting : Siriraj Howpital, Mahidol University, Tertiary care center. Methods : Seventy patients, aged between 45-80 years, ASA physical status I-III underwent unilateral total knee replacement surgery under combined epidural-general anesthesia were recrutied. At the end of surgery, patients were randomized into two groups; ropivacaine (R) and bupivacaine-fentanyl (BF) groups. Patients in the R and BF groups received 0.15% ropivacaine and 0.0625% bupivacaine plus fentanyl 3 ug/ml dellivered by PCEA for 48 hour-postoperative analgesia respectively in a double-blind fashion. Efficacy outcomes as pain visual analogue scale (VAS) score (0-100 mm) at rest and on movement were recorded and analyzed. In addition, safety outcomes were also measured and analyzed. Results : The mean pain VAS score at rest and on movement in this study ranged from 12-30 mm, and 15-40 mm respectively. There were similar on the overall pain over 48 hour both at rest and on movement. The mean difference of overall pain at rest between the R and the BF groups was - 1.71 mm (P=0.58; 95% CI = 4.39 to 7.81) and was - 0.93 mm (P = 0.8; 90% CI = -6.41 to 8.26) for pain on movement. Accumulative mean consumption of PCEA volume in the R group was significantly more than in the BF group at 30 and 48 postoperative hours (P<0.05; and <0.001). More numbers of patients in the BF group experience severe pruritus significantly than those in the R group (P=0.015). There were no significant difference in the other side effects between groups. However, patients in this study considered pain treatment with bupivacaine plus fentanyl significantly beteer quality than with ropivacaine (P=0.02).