Objective: To find out the lowest possible dose of Clonidine that can prolong the total duration of analgesia & duration of sensory and motor anesthesia & analgesia with minimal dose of Bupivacaine without undue side effects. Methods : In this prospective randomized double blind study 60 ASA grade 1 & 2 patients undergoing lower limb orthopedic surgrey were randomly allocated in 2 groups. All received 10 mg heavy Bupivacaine with 50ug of Clonidine in Group A and 75ug of Clonidine in group B for subarachnoid block. Result : Onset of sensory analgesia & motor blockade up to maximal level was achieved faster with 75ug dose sensory (3.6 ± 0.4 min ) & motor (8.6 ± 0.4 min) . The addition of 75mg Clonidine to Bupivacaine, increased. The duration of sensory blockade (224.8±13.2 min) & motor blockade (322.5.±12.6 min) and it also increased the time to first analgesic required (462.8±32.6min). The incidence of postoperative complications was not significantly different vs both groups. Conclusion : 75ug is the preferred dose , in terms of effect versus side effects , when prolongation of spinal anesthesia is desired as in lower limb orthopedics surgeries