Background and objectives: Effective pain management is an important component of intraoperative and postsurgical care; it can prevent pain related clinical complications and improve the patient quality of life. This prospective, randomized, double-blind study was designed to evaluate analgesic efficacy of adding magnesium and midazolam to epidural bupivacaine in patients undergoing total knee replacement. Methods: 120 patients ASA I and II, undergoing total knee replacement surgery were enrolled to receive either bupivacaine 0.5 % or bupivacaine 0.5 % plus magnesium sulphate 50 mg as an initial bolus dose followed by a continuous infusion of 10 mg/h or bupivacaine 0.5 % plus midazolam 0.05 mg/kg as intraoperative epidural analgesia. Postoperatively, all patients were equipped with a patient-controlled epidural analgesia device. Heart rate, mean arterial pressure, oxygen saturation, respiratory rate, pain assessment using a visual analogue scale (VAS),sedation score, patients’ first analgesic requirement times and postoperative fentanyl consumption were recorded. Results: The intraoperative VAS was significantly less in magnesium and midazolam groups. Whereas, in the first postoperative hour, VAS was significantly less in magnesium group. The postoperative rescue analgesia as well as the PCEA fentanyl consumption was significantly reduced in magnesium group. Conclusion: Co-administration of epidural magnesium provides better intraoperative analgesia as well as analgesic-sparing effect on PCEA consumption without increasing the incidence of side-effects.