Background:Dexamethasone as an adjuvant to bupivacaine and ropivacaine for supraclavicular brachial plexus (SCBP) block prolongs motor and sensory blockade. However, comparison of effect of dexamethasone (8 mg) when added to these two local anesthetics has not been well studied. This study was conducted to compare analgesic efficacy of dexamethasone as adjuvant to bupivacaine and ropivacaine in SCBP block.Subjects and Methods:Nerve stimulator-guided SCBP block was given to 120 patients, randomly assigned to one of four groups: (n = 30 in each group) Group B, BD, R, and RD received 30 ml (0.5%) bupivacaine + 2 ml saline, 30 ml (0.5%) bupivacaine + dexamethasone 8 mg, 30 ml (0.5%) ropivacaine + 2 ml saline, and 30 ml (0.5%) ropivacaine + dexamethasone 8 mg, respectively. Time for request of the first rescue analgesic, 24-h analgesic consumption, and different block characteristics were assessed. Student's t-test, Chi-square test, ANOVA were used for statistical analysis.Results:Dexamethasone significantly prolonged time for request of the first rescue analgesic of both ropivacaine (1211.83 ± 32.86 vs. 283.17 ± 7.71 min){ p R, RD < 0.001} and bupivacaine (1205.17 ± 34.32 vs. 364.67 ± 16.50 min) {p B, BD < 0.001}. 24-h requirement for rescue analgesics was more in Groups B and R when compared to Groups BD and RD. The increase in duration of analgesia was more when Groups R and RD (928.66 min) were compared than Groups B and BD (840.5 min). Similar results were seen with onset times and duration of sensory and motor block.Conclusion:The addition of dexamethasone to bupivacaine and ropivacaine in SCBP block prolonged time for first rescue analgesia and reduced the requirement of rescue analgesics with faster onset and prolonged duration of sensory and motor block, with the effect being stronger with ropivacaine.