Zinc sulfide (ZnS) nanoparticles and zinc sulfide/polyvinyl alcohol (ZnS/PVA) composite films of different crystalline sizes have been synthesized by chemical route. The XRD study shows formation of ZnS nanocrystals, having size between 2-4 nm. ZnS nanocrystals exhibit cubic zinc blende crystal structure, while the ZnS/PVA nanocomposite films show wurtizite crystal structure with hexagonal phase. Optical absorption spectra show the blue shifted absorption edge. Photoluminescence (PL) was excited by three different wavelengths. The PL studies of ZnS nanoparticles show the three peaks at 450, 480, and 525 nm and the PL spectra of ZnS/ PVA nanocomposite film show highly broadened emission band in violet-blue region. The emission may be attributed to the presence of sulfur vacancies in the lattice. The PL intensity is found to increase by reducing the particle size. The electroluminescence studies of ZnS nanoparticles and ZnS/PVA nanocomposite films show lower turn on voltage and higher brightness for smaller nanoparticles. The electroluminescence spectra of ZnS/PVA nanocomposite films show violet-blue light emission with two peaks at 425 and 480 nm.