Abstract ZnO nanoparticles have been synthesized by a low-temperature colloidal chemistry method using ethylene glycol as the reaction medium. Crystalline ZnO nanoparticles were formed at a temperature as low as 150 °C. The crystallite size of the ZnO nanoparticles ranged from 8 to 20 nm. The synthesized ZnO nanoparticles exhibited size-dependent photoluminescence. Photoluminescence of the ZnO nanoparticles depended largely on the post-annealing temperature. Both DL and UV emissions were suppressed at a lower post-annealing temperature of 300 °C; however they were recovered at a higher annealing temperature of 900 °C.