Objective: of this study is to assess the quality of spinal anesthesia block and observe hemodynamic changes occurring during c-section, comparing two different baricities of bupivacaine i.e. 0.5% isobaric and 0.75% hyperbaric in same doe and volume. Design: Quasi experimental study. Place and Duration of Study: Department of Anesthesiology and ICU, Shalamar Hospital, Lahore, from April 2007 to October 2007. Patients and Methods: Sixty, adult patients of ASA I and II, undergoing elective lower segment cesarean section were included in this study. The patients were randomly divided into two groups, Group-I received isobaric 0.5% bupivacaine 2.5 ml (12.5 mg) and group-II received Hyperbaric 0.75% bupivacaine 2 ml in which 1 ml of CSF was added and then 2.5 ml injected (12.5 mg), so that both groups receive equal volume and dose of bupivacaine but different baricities. Quality of block was assessed by pin prick and Bromage Scale for sensory and motor block respectively. Hemodynamic changes were compared with the base line readings. Results: No significant difference was found between the two groups regarding the quality of block but there were significant hemodynamic differences, in group-I, initial maximum increase in heart rate and decreases in MAP were observed at 2 minutes. While in group-II, maximum increase in heart rate was observed immediately after injection and maximum decrease in MAP was at 2 minutes. This shows that there was immediate decrease in MAP, which may be due to faster onset of sensory block in group-II, when compared with group-I. Conclusion: No significant differences were found between the two groups regarding the quality of block. But the rapid onset of sensory block with 0.75% hyperbaric bupivacaine in group 11 produced more hypotension, when compared with 0.5% isobaric bupivacaine in group 1 but it was not statistically significant.