Photolabile property of ferrocyanide ion is well known. The electron generated by ferrocyanide ion on exposure to light may be utilized for the photoreduction of dye. In the present work, use of photo labile nature of ferrocyanide ion has been made for photocatalytic bleaching of bismark brown dye. Copper hexacyanoferrate (II) was synthesized and used for this purpose. Effect of different parameters like pH, concentration, light intensity etc .has been observed on the rate of photocatalytic bleaching. A suitable mechanism for the phototcatalytic degradation of bismark brown dye has been proposed.