The polarographic reduction of 2-hydroxy-3-methoxy-5-(2-propenyl) azobenzene in Britton Robinson Buffer with pH range 3 and 12 at room temperature has been investigated in aqueous solution of ratio 1:1. Two straight lines were obtained from the Ep-pH plots for the compound. Using the pH dependence of the polarographic and voltammetric behaviour of the azo compound the pKa value was determined to be 10.70 ± 0.02 and 11.08 ± 0.02, respectively. An electrode reaction mechanism for the azo compound has been suggested. The determination limit has been found as 1 x 10-7 M.