Abstract ZnS:O2− (ZSO) nanoparticles were synthesized using a low temperature solid-state reaction method. The effects of annealing conditions and the content of the surfactant polyethylene glycol (PEG) on photoluminescence (PL) properties of the ZSO nanoparticles were studied. It was found that annealing and adding PEG during the synthesis did not change the crystal structure of ZSO nanoparticles, and their average crystallite size increased with increasing annealing time and temperature, but decreased with increasing PEG content. The emission intensity of ZSO nanoparticles was found to be enhanced after annealing or using PEG during the synthesis. Optimal annealing conditions both in air and vacuum and the optimal content of PEG were obtained for achieving maximum emission intensity from the ZSO nanoparticles.