Background: Regional anesthesia is the preferred technique for most of abdominal and lower limb surgeries. This study was designed to evaluate the effects of intravenous dexmedetomidine on spinal anesthesia with 0.5% hyperbaric bupivacaine. Materials & Methods: The present study consisted of 160 patients of ASA Grade I & II patients planned for orthopedic lower limb surgeries under sub arachnoid block. . Patients randomized into two equal groups of 80 patients each. Drugs prepared by the same person throughout the study, involved only in group allocation and drugs administration. Drugs for both groups prepared in two 50 ml syringes- one for loading dose (labelled L) and other for maintenance dose (labelled M). Results: The duration of onset of sensory blockade was 7.0 [6.0-7.0] minutes in group I and 6.0 [6.0-7.0] in group II. The duration of onset of motor blockade was 3.0 [3.0-4.0] minutes in both the groups. There was no statistically significant difference in the mean duration of onset of sensory and motor blockade of the subjects belonging to two groups (p value >.05). The sedation score was 2.5 [2.0-3.0] in group I and 3.0 [2.0-3.0] in group II. The duration of recovery from sensory blockade was 210.0 [180.0-210.0] minutes amongst group I subjects whereas it was 165.0 [150.0-180.0] minutes amongst group II subjects. The duration of recovery from motor blockade was 232.5 [210.0-240.0] minutes amongst group I subjects whereas it was 180.0 [180.0-210.0] minutes amongst group II subjects. The difference was significant (P< 0.05). There was significant difference in post-operative pain in both group (P< 0.05). Conclusion: Intrathecal dexmedetomidine prolongs the effect of subarachnoid anesthesia with arousable sedation.