Tin monosulfide (SnS) was prepared via DC magnetron sputtering on glass substrates and annealed at two temperatures (200, 300) ºC. The annealing effect on crystallinity, optical and gas sensing characteristics of Tin monosulfide films were examined. The morphology and structure of creating SnS thin films have been researched via scanning electron microscopy (SEM), X-ray diffractions (XRD), and Atomic Force Microscopy (AFM). XRD results explain that the increasing annealing temperature from 200ºC to 300ºC caused an increase in crystallite size, while the Microstrain and the dislocation density were reduced. SEM showed that the increasing in the SnS cluster distribution with particle size increases with increasing the annealing temperature. Optical properties prove that the energy gap decreases 2.185 eV to 1.967 eV as the annealing temperature increases from 200oC to 300oC, and the annealed samples exhibited enhanced gas sensitivity up to 75%.