ZnO sub-microspheres were synthesized via a new, simple, and one-step method by using zinc acetate dihydrate as a precursor and PEG200 as a solvent and modifier. The effect of temperature (160-210 A degrees C) on the crystallization, surface morphology, and luminescence properties of ZnO spheres was investigated using different characterization techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV-Vis spectroscopy, and room temperature photoluminescence. The results show that the ZnO crystal has a hexagonal wurtzite structure. The products have monodispersed spherical morphology with diameters in the range of 200-600 nm. They have intensive UV emission peaks at similar to 380 nm and relatively weak and broad green peaks at similar to 550 nm. The PEG200 molecules adsorb on the surface of ZnO spheres. On the basis of the experimental results, a mechanism was proposed to elucidate the formation of ZnO sub-micron spheres.