An attempt has been made to enhance the photocatalytic activity of bismuth ferrite by doping it with cobalt, to prepare a catalyst to use in wide pH range for the photodegradation of Evans blue dye. The progress of the reaction has been monitored spectrophotometrically by measuring the absorbance of the reaction mixture at definite time intervals. Different parameters such as pH, the concentration of dye, amount of semiconductor and light intensity were varied to achieve the optimum rate of photodegradation. The results show that doping of bismuth ferrite by cobalt increases the rate of photocatalytic degradation due to narrowing of the band gap. Undoped bismuth ferrite has the highest catalytic activity in basic while the Co-doped catalyst in acidic medium. A tentative mechanism for the reaction has been proposed.