Background: Lower limb surgery refers to surgical procedures performed on the lower extremities of the body, which include the hips, thighs, knees, legs, ankles, and feet. The present study compared intrathecal dexmedetomidine and magnesium sulfate as adjuvants to bupivacaine in total hip replacement. Materials & Methods: 90 patients selected for total hip replacement surgery under spinal anaesthesia were divided into 3 groups. Patients in group I received 15 mg hyperbaric bupivacaine and 0.1 ml (10 μg) dexmedetomidine, in group II received 15 mg hyperbaric bupivacaine and 0.1 ml (50 mg) magnesiumsulfateand in group III received 15 mg hyperbaric bupivacaine and 0.1 ml normal saline as control. Parameters such as onset times of sensory blocks, motor blocks, regression timeof sensory blocks and motor blocks were compared. Results: The mean height in group I patients was 159.4 cm, in group II was 161.2 cm and in group III was 159.4 cm. The mean weight was 65.2 kgs in group I, 64.2 kgs in group II and in group III was 63.4 kgs. The mean BMI was 21.3 kg/m2 in group I, 22.8 kg/m2in group II and in group III was 23.0 kg/m2. The difference was non- significant (P> 0.05). The mean onset of sensory block was 2.4 minutes, 6.2 minutes and 4.9 minutes, onset of motor block was 3.5 minutes, 7.1 minutes and 4.7 minutes, regression time of sensory block was 321.4 minutes, 242.4 minutes and 194.2 minutes and regression time of motor block was 346.2 minutes, 236.4 minutes and 182.6 minutes in group I, II and III respectively. The difference was significant (P< 0.05). Conclusion: In contrast to intrathecal Mg, intrathecal dexmedetomidine augmentation of spinal block results in faster onset and longer duration of sensory and motor block.