In this research ZnO and Zn1-xAlx (x =1, 3, 5, 7% mol) nanoparticles were synthesized by sol-gel method. The effect of Al concentration on the structure, morphology, absorption spectra and photocatalytic properties investigated by using X-ray, TEM, EDS and UV-Vis spectrophotometer approaches. Hexagonal, spherical and rod-like structure was achieved as the dominant structure for undoped nanoparticles, low and high concentrations of doped Al, respectively. Photocatalytic activity of nanoparticles was measured by degradation of methyl orange as a pollutant under radiation of ultraviolet (UV). The experimental test results indicate that the best photocatalytic performance is at of 5% of Al. Furthermore, the doped ZnO nanoparticles have more activity in visible area compared with undoped nanoparticles. The absorption amount in this area increases by raising the AI concentrations. Furthermore, the band gap of the particles decreases from 3.22 eV to 2.93 eV by increasing Al percentage. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology japan. All rights reserved.