Abstract: The electroreduction of bromocresol purple was studied by d.c.polarography, differential pulse polarography and cyclic voltammetry. Three or four polarographic reduction waves (peaks) appeared at different pH. First three waves were observed over pH range of 2—9. When pH<9 waves Ⅱ and Ⅲ were overlapped with an appearance of a new wave Ⅳ. Wave Ⅰ was a diffusioncontrolled, irreversible, two electron one, the E_1/2(E_p) of which shifted towards more negative potentials with increasing pH. Wave Ⅱ was so small, it could be seen only in differential pulse polarograph.Wave Ⅲ being adsorptive in nature was an irreversible, two-electron one, the E_1/2 (E_p) of which was independent of pH.Wave Ⅳ was a diffusion controlled, two-electron one. Considering acidbase equilibrium of both oxidized form and reduced form,a formula expressing the relationship between pH and E_1/2 has been derived, and the plot of pH-E_1/2 for wave Ⅰ has been explained. The mechanism for the reduction of bromocresol purple is discussed.