The photocatalytic decolorizations of aqueous solutions of Reactive Red 2 dye in the presence of ZnO suspension has been investigated with the use of artificial UV-A light sources. The effects of various parameters, such as time of irradiation, photocatalyst amount, pH, addition of H2O2 and temperature on photocatalytic degradation were investigated. The rate of decolorization was found to increase significantly with time of irradiation. Under optimal conditions, the extent of decolorization was 100% after 30 minutes of irradiation. Optimum catalyst concentration [Catalyst]Opt was measured and found equal to 2.5 g L-1. The oxidizing agents such as oxygen and hydrogen peroxide enhance the decolorization rate. However the addition of more amount of hydrogen peroxide decreases the rate of decolorization. The optimum pH for the photocatalytic decolorization of Reactive Red 2 dye in the presence of ZnO suspension is pH 10.0. Photocatalytic decolorization was found to increase with increasing temperature. Arrhenius plot shows that the activation energy is equal to 10.130 ± 1 kJ mol-1.