Thin films of Sb2S3 were prepared by flash evaporation. As-deposited films were found to be amorphous and highly resistive (R>10(6) Ohm) in nature. An amorphous-crystalline phase transition occurs at 498 K on subsequent annealing in nitrogen atmosphere. The fundamental optical transition is direct in nature and the optical band gaps (E-g) lie in the region 1.70-2.07 and 1.42-1.65 eV for amorphous and crystalline films, respectively. A near-linear decrease in E-g with decreasing S/Sb ratio was observed suggesting the dependence of the band gap on film composition.