Indium sulfide (In2S3) films have been deposited on soda-lime glass substrates using a spray technique (CSP). Indium chloride and thiourea were used as precursors at a molar ratio of S:In = 2. The substrate temperature was fixed at 340°C. The effect of film thickness on the structural, morphological and optical properties of the as-deposited films has been studied. These films were char- acterized by x-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical absorption spectroscopy. As-prepared samples were polycrystalline with a cubic structure and (400) as preferential orientation. Their grain size increased from 35 nm to 41 nm with increasing thickness whereas the dislocation density and microstrain of the films de- creased with the increase of thickness. Both SEM and AFM images showed that the films were homogenous with an increase of the surface roughness with the increase of thickness. The optical transmittance of the films de- creased from 80% to 20% in the visible and infrared regions when the thick- ness was increased from 0.78 lm to 6.09 lm. The optical band gap Eg was found to be in the range of 2.75–2.19 eV and showed a decrease with film thickness. Based on the measured optical constants (n and k), a Wemple– Didomenico model was used to determine the values of single oscillator energy (E0), dispersion energy (Ed), optical band gap (Eg) and high frequency dielec- tric constant (e1). In addition, these films exhibited n-type conductivity and were highly resistive. These results confirm that In2S3 thin films are a promising alternative as a buffer-layer material for CuInGa(S,Se)2-based solar cells.