Background and objectives: To evaluate the efficacy of Dexmedetomidine as an adjuvant to 0.25% Bupivacaine in the femoral nerve block for postoperative analgesia following unilateral total knee replacement under spinal anaesthesia. Methodology: 60 patients who were posted for TKR taken up for our study after obtaining written informed consent. Femoral nerve block was administered under ultrasound guidance once the sensory level recedes to T12 dermatome. Here, patients were randomly allocated into two groups (A&B) using a computer-generated randomization chart. Patients in group A received 20ml of 0.25%Bupivacaine with Dexmedetomidine (0.5 mcg/kg) made up to 1ml (total 21ml). Patients in group B received 20ml of 0.25% Bupivacaine with 1ml normal saline (total 21ml). Pain was assessed using VAS, Motor power of lower limb was recorded with MBS and vitals are closely monitored. All the observations are tabulated and statistically analyzed. Results: In group A the mean duration of analgesia is 16.73(±1.14) and in group B the mean duration of analgesia is 11.3(±1.15), P value is statistically significant. Conclusion: Dexmedetomidine as an adjuvant to Bupivacaine prolongs theduration of analgesia in femoral nerve block after unilateral total kneereplacement.