Nano-sized ZnO powder with crystallite size in the range 12 to 50 nm were prepared by solution combustion route. The product was characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Photocatalytic degradation of rhodamine B (RB) dye was carried out with ZnO nanopowder. The effect of parameters such as the crystallite size, amount of catalyst, concentration of the dye, pH and irradiation on photocatalytic degradation of RB is studied. The results reveal that the maximum decolorization (more than 95%) of dye occurred with ZnO catalyst in 8 min of stirring at basic pH under solar light irradiation. It was also found that chemical oxygen demand (COD) reduction takes place at a faster rate under solar light as compared to that of UV light. The results suggest that, the ZnO solar photocatalytic irradiation is better than the calcined ZnO/solar and UV light irradiation. (C) 2011 Published by Elsevier B.V.