A simple method for the determination of quinidine sulfate in tablets is based on the formation of an ion-pair between quinidine Comand thymol blue (TB) at pH=5.5 in aqueous-methanol solution. The absorbance of the ion-pair formed is measured and the Colncentration of the drug is calculated. The molar ratio of the ion-pair is determined and found to be 2:1 and with general formula [Q]⁺⁴ 2.[T.B]^-1 SO₄^-2 HSO₄^-1 as  calculated by elemental analysis. Using the present method quinidine sulfate in tablets was assayed. The results were statistically compared with those obtained by the official method.