A ZnS nanoparticle was prepared using hydrothermal interaction of zinc acetate with Thiourea in different reaction temperatures (170oC, 180oC, 185oC, 190oC). The structural characterization of synthesized nanoparticle was determined by X-ray diffraction (XRD) which showed a hexagonal structural of ZnS. Scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) analysis were confirmed that the morphology and elemental analysis was formed ZnS nanoparticle. Absorption study has been carried out using UV-VIS spectrophotometer to determine the band gap of ZnS nanoparticle. The optical energy band gap was changed at values equal to (4.16, 4.46, 4.1 and 4.35eV) with different hydrothermal temperatures at (170oC, 180oC, 185oC and 190oC) respectively. However, these values of energy gaps for ZnS nanoparticles are blue shift and larger than that bulk value due to quantum confinement. Fourier Transform Infrared Spectra (FTIR) is recorded in an FTIR spectrometer to verify the presence of ZnS powder. The particle size of ZnS calculated was ranged between 3.5 to 3.9 nm according to Sherrer's equation and the results were compatible when using Effective Mass Approximation (EMA).