Today, absorber layers such as CIGS and CdTe are frequently used in thin film heterojunction solar cells. However, it is an important problem that these materials contain rare, expensive and toxic elements such as In, Ga, Cd and Se. Additionally, commercialization limits have been reached for CIGS and CdTe based solar cell devices [1,2]. At this point, it is thought that Cu2ZnSnS4 (CZTS) films can be preferred as an alternative material to these films. However, CZTS films contain four different elements which increases the probability of secondary phase formation that negatively affect device performance [3]. As an emerging solar cell absorber, antimony trisulfide (Sb2S3) films have the potential to solve these problems with their structure consisting of two elements that are abundant in nature [4]. Previous researches on thermally evaporated Sb2S3 films have shown that these films generally form amorphous in initial production and the optical band gap value remains high for an absorber layer to be used in solar cell applications [5-7]. In this study, Sb2S3 thin films have been deposited by thermal evaporation method on glass substrates under high vacuum. After the evaporation, as-deposited films were heat-treated by annealing in N2 atmosphere at 300 and 350 °C, during 60 min in a quartz tubular furnace. Structural and optical properties of the films have been investigated in detail with the help of Raman spectroscopy and UV-VIS Spectroscopy. After annealing, it was observed that the films changed from amorphous to crystalline structure and the optical band gap values could be reduced from 2.23 eV to 1.71 eV.