Optical and scintillation properties of pure ZnS single crystal were examined. ZnS showed ∼70% optical transmittance in wavelength longer than 350 nm. In X-and α-ray induced radioluminescence spectra, intense emission peaks at 440 and 520nm were observed. The origin of the former and the latter emission peaks were ascribed to zinc vacancy and sulfur vacancy, respectively. The temperature dependence of X-ray radioluminescence was investigated and intensities of both emission peaks monotonically decreased in higher temperatures. Finally, the absolute scintillation light yield of pure ZnS turned out to be 500 photons/5.5MeV-α.