Ultrasonic irradiation method was applied for preparation of Sb-doped ZnO nanostructures (0 <= mol fraction of Sb+3 ions <= 0.15) in water at 60 min without using any organic compound and additional post treatment. The nanostructures were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and UV-vis diffuse reflectance spectroscopy (DRS) techniques. The results showed that the doping greatly changed morphology and size of the pure ZnO. Photocatalytic degradation of methylene blue (MB) on the nanostructures under UV irradiation and effects of various operational parameters were investigated. The results reveal that the maximum degradation occurs on the nanostructures with 0.03 mol fraction of Sb+3 ions. The rate constant increases with irradiation time up to 60 min and then decreases. The photocatalyst with 0.4 g/L have highest degradation rate constant. Moreover, the degradation rate constant decreases with calcinations of the nanostructures. The nanostructures have highest photocatalytic activity at pH 5.4. (C) 2013 Elsevier B.V. All rights reserved.