Antimony trioxide (Sb2O3) thin films were prepared by thermal evaporation under vacuum technique, using Sb2O3 powder as evaporate onto glass substrates. The substrate temperature was varied from 323 to 473 K and structural and optical properties of the films were studied. The structural studies of the Sb2O3 thin films indicates the presence of the ?- Sb2O3 with predominant cubic phase. The energy band gap of Sb2O3 thin films was determined from the absolute values of the measured transmittance by assuming a direct transition between valence and conduction band of Sb2O3 thin films.