The present work investigates the surface morphology and optical characteristics of 80 nm Al2O3(alumina) thin films deposited on Si (100) at room temperature and then annealed at 600 and 800 °C. Atomic force microscopy (AFM) analysis depicts that there is no prominent change in the average size of particles when the as-deposited film is annealed at 600 °C, whereas at 800 °C an increase in the size of particles is observed. In addition, alumina film annealed at 800 °C has the most uniform and dense particle distribution. Moreover, the RMS roughness of the alumina film also increases from 1.8 to 2.4 nm with annealing temperature. The optical energy gap, estimated using diffuse reflectance spectra, increases from 4.4 to 5.3 eV after annealing the film at 800 °C. These values of optical energy gap are also confirmed with spectroscopic ellipsometry. The refractive index also increases with annealing, suggesting that the film becomes denser after annealing. A spectroscopic ellipsometer is used to extract the dielectric constant, and dielectric loss of Al2O3 film using the Tauc Lorentz model. The dielectric constant of alumina thin films is also found to increase with annealing. In addition, the obtained variation in surface morphology with annealing is correlated further with changes in optical parameters. Our experimental study reveals that the morphology and optical characteristics of Al2O3 film are significantly affected by the annealing temperature making them suitable as an antireflection coating in solar cells.