Thin films of zinc nickel sulphide (ZnNiS) were grown on glass substrates using the chemical bath deposition (CBD) technique at room temperature. Effects of ion concentration of NiCl2 on the film’s optical and structural properties were investigated. This was achieved by measuring the optical absorbance of the films at normal incident light in a wavelength range of 200–1000 nm with a Janway 6405 UV–VIS spectrophotometer. Other properties, such as transmittance, reflectance, thickness, and energy gap, were calculated from the measured absorbance values. The low reflectance and large band gap properties make the film a good material for anti-reflection coating and absorber layer of solar cells, respectively. The films grown were further characterized using an X-ray diffractometer and an optical microscope to determine the structural properties. From the XRD results, the film crystal structure was found to be cubic. The lattice constant and grain size of the grown films were found to be 5.420 Ǻ and 0.31 μm, respectively.