The dependence of the magnetic properties of pure ZnO and Zn1-xNixO with x = 0.01, 0.02, 0.03, 0.04, 0.05, 0.08 and 0.1 on their particle size has been investigated. For this purpose, three kinds of ZnO samples, namely nanoparticles (36 nm), micrometer particles (0.2 mu m) and bulk (grain 7.5 mu m) have been made. Also, the Zn1-xNixO with x= 0.01, 0.02, 0.03, 0.04, 0.05, 0.08 and 0.1 nanoparticles were synthesized by a simple and affordable mechanochemical method. The results showed that the pure ZnO nanoparticles with an average particle size of 36 nm in the magnetic field from zero to about 2000 Oe represented ferromagnetic property, while ZnO particles with an average particle size of 0.2 mu m and grain size of 7.5 mu m (Bulk) showed paramagnetic and diamagnetic behaviors in different applied magnetic fields, respectively. Also, the Ni doped ZnO nanoparticles showed ferromagnetic behaviors in the magnetic field up to about 2000 Oe. (C) 2017 Elsevier Ltd. All rights reserved.