The effect of transition metal ions such as Mo (VI) doped ZnO has been investigated for photocatalytic bleaching of eosin Y. Doped samples were synthesized by stirring and microwave exposure. The effect of concentration of dopant on the rate of photocatalytic bleaching of dye has also been observed. The rate of photocatalytic blea ching of dye increases with increase in concentration of dopant up to a certain limit with all these metal ions, but decreases after further concentration of dopants. A tentative mechanism has been proposed.