Gallium nitride thin films were grown by pulsed laser deposition. Subsequently, post-growth annealing of the samples was performed at 400, and 600 oC in the nitrogen atmosphere. Surface morphology of the as-grown and annealed samples was performed by atomic force microscopy, surface roughness of the films improved after annealing. Chemical analysis of the samples was performed using x-ray photon spectroscopy, stoichiometric Gallium nitride thin films were obtained for the samples annealed at 600 oC. Optical measurements of the samples were performed to investigate the effect of annealing on the band gap and optical constants the films.