Low temperature (25 degrees C-80 degrees C) synthesis of zinc oxide (ZnO) nanoparticles (<20 nm) at short synthesis periods (similar to 30 min) was achieved by precipitation. The precipitation system was formed using zinc acetate dihydrate as zinc source, ethylene glycol (EG) as solvent and polyvinyl pyrrolidone (PVP) as chelating agent. The size of spherical ZnO nanoparticles was manipulated by the choice of precipitation temperature (13.0 +/- 1.9 nm at 25 degrees C and 9.0 +/- 1.3 nm at 80 degrees C), which essentially changes the nature of adsorption events between ZnO crystals and organic molecules. The particle size can also be regulated by the amount of chelating agent as a result of further enhancement in adsorption between ZnO crystals and organic additives. The spherical ZnO nanoparticles were agglomerated into triangular form when different solvent was used - by substituting water for EG, which has different adsorption ability. Accordingly, formation and growth mechanisms controlling the size and morphology of ZnO nanoparticles have been proposed.