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 acid-base 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.