The studies on luminescent II-VI semiconducting nanomaterials have attracted widespread attention, due to their potential applications in optoelectronic and biophotonic devices. Amongst II-VI group semiconductor nanoparticles, ZnS Nano Particles with large exciton binding energy and wide direct bandgap at room temperature have drawn considerable attention for exploring its interesting optoelectronic properties. In this paper, high band gap Zinc Sulphide nanocrystals are prepared by simple Co-precipitation method at different concentrations of precursors, and the role of sulphur concentration on structural and optical properties is studied. The Zinc Sulphide nanomaterial was prepared using low cost precursors and de ionised water as solvent without using any capping agents. As synthesized Zinc Sulphide nanocrystals were characterized by using X-ray diffraction (XRD), Energy Dispersive Spectroscopy analysis, UV-Visible Spectrophotometry, Photoluminescence, Scanning electron Microscopy (SEM) and Ellipsometry. X-ray diffraction studies revealed that as prepared of ZnS nanocrystals are Polycrystalline with Cubic phase with preferential orientation along (111) direction. The crystallite size of the order of 5-11nm were obtained. EDAX pattern confirms the presence of Zinc and Sulfur. From optical absorption measurements, it has been observed that the direct optical band gap energy increases from 4.4 to 5.2eV with decrease in sulphur concentration in ZnS and exhibit large quantum confinement effect. Ellipsometry was carried out to measure optical constants of ZnS thin film. The electrical conductivity of the film is measured for the film coated on ITO glass by two probe methods. Copyright © 2017 VBRI Press.