Sb 2 S 3 thin films are obtained by evaporating of Sb 2 S 3 powder onto glass substrates maintained at room temperature under pressure of 2ร10 -5 torr. The composition of the thin films was determined by energy dispersive analysis of X-ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). The asdeposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as-deposited and annealed Sb 2 S 3 thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400-1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E 0 , dispersion energy, E d ) were determined. The static refractive index n(0), static dielectric constant, ฮต โ , and optical band gap energy, E g , were also calculated using the values of dispersion parameters.