gamma-MnS thin film was deposited at 40 degrees C temperature on glass substrate by Chemical Bath Deposition (CBD) method that has superior advantageous in terms of fast and cheap production. MnS thin film was annealed in nitrogen atmosphere at temperatures 100, 200, 300, 400, 500 C for an hour. The effect of annealing temperature on structural and optical properties have been investigated. X-ray diffraction (XRD) analysis revealed that gamma-MnS thin film had the phase change and oxidized at 400,500 C annealing temperature. The grain size of the annealed film was calculated between 241 and 280 angstrom as a function of annealing temperature. It was observed that optical transmission values decreased at wavelength of 400-700 nm (visible region) after annealing at temperatures 400 and 500 degrees C. Increasing annealing temperature induces reduction in energy band gap values from 3.89 eV down to 3.46 eV. Refractive index (n) values were calculated by envelope method: Refractive index values at visible region increased from 2.03 to 2.54 with increasing annealing temperature. (C) 2018 Elsevier GmbH. All rights reserved.