Objective. The ideal local anesthetic solution for intrathecal use has rapid onset and reliable duration, with less incidence of adverse events. This study was aiming to compare the onset of anesthesia and duration of action of isobaric and hyperbaric bupivacaine for subarachnoid block (SAB).Methods. Sixty patients who underwent lower abdominal, hips, and lower extremity surgeries were randomized into two groups. Group I received 20 mg of 0.5% isobaric bupivacaine, while Group H received 20 mg of 0.5% hyperbaric bupivacaine. Injection was made intrattecally in midline position at L3-4 interspace in sitting position.Results. The onset of analgesia and motor blocks with isobaric was faster when compared to hyperbaric bupivacaine (4.8 ± 2.2 versus 7.5 ± 2.2 minutes and 4.1 ± 2.1 versus 6.4 ± 2.4 minutes, resp.,P<0.001). The duration of sensory and motor blocks was longer in isobaric when compared to hyperbaric bupivacaine (276 ± 30 versus 163 ± 22 minutes and 266 ± 32 versus 163 ± 24 minutes,P<0.001). In both groups, hemodynamic changes were not clinically relevant, and the adverse effects were comparable.Conclusion. Isobaric produced more rapid onset and longer duration when compared to hyperbaric bupivacaine.