This paper reports the synthesis of ZnO nanostructures (nano-bullets, nanorods, nanospheres) by a facile and novel modified polyol method without surfactants, varying only the molar concentration of precursor salt (Zinc acetate dihydrate) using ethylene glycol and deionized water. At a constant temperature of 160 degrees C, nano-bullets were obtained at a concentration of 0.6 M, whereas at 0.8 M nanorods were observed while at 1.0 M only nanospheres appear. X-ray Diffraction, Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy and Room-Temperature Photoluminescence properties were used to characterize the nanostructures. Based on the results it is suggested a high dependence between morphology and molar concentration of the precursor salt as well as a mechanism of crystallization of the different nanostructures. The nanostructures may be used to produce optoelectronic devices. (C) 2017 Elsevier Ltd. All rights reserved.