The wurtzite phase of ZnS nanocrystal has been prepared by annealing in 200–600°C temperature range, its cubic phase of 2–3nm size, prepared through soft chemical method. Results of isochronal experiments of 2h at different temperatures indicate that visible transformation to wurtzite from cubic ZnS appears at a temperature of 400°C, which is about three times smaller than that of bulk ZnS phase transition temperature. The phases, nanostructures, and optical absorption characteristics are obtained through X-ray diffraction, transmission electron microscopy, and UV–visible absorption spectroscopy. A stable and green photoluminescence emission peaked at 518nm is observed from the 600°C annealed samples, under ultraviolet light excitation.