Spinal anaesthesia is commonly used for abdominal and lower limb surgeries. This study has been designed to evaluate the addition of two doses of dexmedetomidine(10μg and 15μg) as an adjuvant to 0.5% hyperbaric bupivacaine 3ml intrathecally for elective abdominal and lower limb surgeries. Methods: In this randomized, double-blind prospective study, 60 patients of ASA I and II were randomized to three groups: group I, II and III(n=20). All patients received a drug volume of 3.5ml containing 3 ml hyperbaric bupivacaine(15 mg). They received dexmedetomidine 10μg (Group II) or 15 μg (Group III) added to bupivacaine ; the control group (Group I) received 0.5ml of 0.9% saline added to bupivacaine. Results: It was found that the onset of sensory block upto T10 and motor block is significantly faster in group II (174 sec and 109.5 sec) and III (93 sec and 57.75 sec) over group I (294 sec and 155.25 sec).The mean time for two segment regression and sensory regression to L1, the mean duration of analgesia and motor blockade is significantly prolonged in Group III(138.75 min,469.5 min,438 min,510.5 min) over Group II (104.25 min, 321 min,277.5 min, 323.25 min) and Group II over Group I(88.5 min,257.25 min,238.5 min,265.5 min) (p<0.001). Conclusion: I conclude that 15μg of dexmedetomidine added to local anaesthetic in subarachnoid block has proved to be a better adjuvant in prolonging the sensory and motor blockade and the duration of postoperative analgesia.