During the past few years, a pilot-scale spray pyrolysis set-up able to produce large quantities of submicronic powders (1kg/day) has been assembled in our laboratory. During the process, droplets of a precursor solution are dried and decomposed to the required compound. The presence of an additional soluble flux in the precursor solution permits to obtain agglomerate - free nanoparticles after washing the product. Therefore, pure zinc oxide nanoparticles have been successfully synthesized by adding lithium or sodium nitrates to the initial zinc nitrate solution. The nanoparticles have been characterized by X-ray diffraction, field-emission scanning electron microscopy, laser scattering size analyzer. The influence of the precursor solution composition and of the operating parameters on the morphology and the average size of ZnO nanoparticles is discussed.