Transmission electron microscopy was applied to study structural changes of InN films grown by molecular beam epitaxy on c-sapphire substrates with a GaN buffer layer. The films were studied as-grown and also following by rapid thermal annealing, irradiation with 2MeV He+ ions, and annealing after irradiation. Defects formed after each procedure were discussed. The results of these studies show that randomly distributed extended defects, formed upon irradiation, can come to uniform distribution throughout the samples upon annealing. An irradiation by 2MeV He+ ions followed by thermal annealing at 425 and 475 1C leads to the unusual increase of the electron mobility of these films. Annealing at 500 1C led to the formation of In clusters and delamination of the film from the substrates.