Abstract Bismuth sulfide (Bi2S3) films were chemically deposited by a novel deposition system in which ammonium citrate was used as the chelating reagent. Two sulfur source thioacetamide (TA) and sodium thiosulfate (Na2S2O3) were used to prepare Bi2S3 films. Both the as-prepared films have amorphous structure. However, annealing can improve the crystallization of the films. The composition of the films prepared by TA and Na2S2O3 are all deviate from the stoichiometric ratio of Bi2S3. The Bi2S3 films are all homogeneous and well adhered to the substrate. The optical properties of the Bi2S3 films are studied. The electrical resistivity of the as-prepared films are all around 7 × 103 Ω cm in dark, which decreases to around 1 × 103 Ω cm under 100 mW/cm2 tungsten–halogen illumination. After the annealing, the dark resistivity of the Bi2S3 film prepared by TA decreases by four magnitudes. In contrast, the dark resistivity of the Bi2S3 film prepared by Na2S2O3 only decreases slightly.