The photocatalytic degradation of Rose Bengal has been carried out in the presence of semiconducting zinc oxide. The progress of the reaction is observed photocolorimetrically. The effect of various operating variables like pH, concentration of dye, amount of semiconductor and light intensity on the reaction has also been observed. Attempts have been made to study the effect of addition of some metal ions such as Mn+2, Fe+2, Co+2, Ni+2, Cu+2 and Zn+2. It is found that the added metal ions increase the reaction rate to some extent. It is also reported that Cu+2 is most effective in enhancement of degradation of Rose Bengal. A tentative mechanism has been proposed.