in this study, a simple, rapid and selective method was developed for the determination of dexamethasone. the proposed method is based on inhibitory effect of dexamethasone on the oxidation of orange-g by bromate in sulfuric acid media. the reaction was followed spectrophotometrically at 478.5 nm (?max). under optimum experimental conditions, (72.6 ?mol l-1 of orange-g, 0.76 mol l-1 of h2so4, 0.005 mmol l-1 of bromate, 20 oc and 420 s), calibration curve was linear in a wide range and the limit of detection was comparable to other methods the relative standard deviations of 0.2 and 54.0 mg ml-1 of dexamethasone were 1.04 and 1.03%, respectively .the interfering effect of foreign species were studied. the developed method was suceessfully applied for the determination of dexamethasone in biological and pharmaceutical samples with satisfactory results.