Background: In recent years there has been a increasing interest in the practice of regional anaesthesia especially peripheral nerve blocks for surgical anaesthesia and postoperative analgesia. Imaging guidance for nerve localization helps the promise of improving block success with fewer complications. Among the imaging modalities currently available, ultrasonography seems to be the most suitable for regional anaesthesia. One the most significant advantage of ultrasound technology is the availability to provide anatomic examination of the area of interest. Aim of the Work: To evaluate the additive effect of dexmedetomidine to levobupivacaine in femoral sciatic block in total knee replacement regarding the onset and duration of both sensory and motor blockade, postoperative analgesia requirements. Patients and Methods: After ethical approval, 60 patients aged 40-60 years old, with an American Society of Anaesthesiologists (ASA) physical class I and II who underwent total knee replacement using combined femoral-sciatic anaesthesia, were included in this prospective, randomized,controlled, double-blinded study. Patients were randomly assigned to receive levobupivacaine alone divided (group B) or dexmedetomidine 100 μg added to levobupivacaine (group BD) [n = 30 for each group] for combined femoral–sciatic nerve block. Results: This study showed that the addition of dexmedetomidine 100 μg to levobupivacaine during ultrasound-guided combined femoral-sciatic nerve block for total knee replacement was associated with +50 % longer duration of analgesia, -20% shorter onset times for sensory and motor block, -25% faster time for surgical readiness, and longer duration of sensory and motor block (+45% and +40%, respectively). Unfortunately, the present study found that the addition of 100 μg dexmedetomidine to levobupivacaine during femoral–sciatic nerve block for total knee replacement was associated with bradycardia and hypotension (30% and 10 %, respectively). Conclusion: Addition of dexmedetomidine to levobupivacaine during femoral–sciatic nerve block for total knee replacement was associated with faster onset of sensory and motor block, decrease intraoperative and postoperative requirements of analgesia and longer duration of motor block than levobupvicaine alone.