GaN:In films having the single polarity of (0 0 0 1) were successfully grown on sapphire(0 0 0 1) substrate by plasma-assisted molecular beam epitaxy (MBE). The determinations of polarity were carried out by coaxial impact collision ion scattering spectroscopy (CAICISS). The GaN : In films grown at 600 degrees C with In flux had a single polarity of (0 0 0 1), whereas the GaN:In films grown at 550 degrees C with In flux and the GaN films groan at 600 degrees C without In flux consisted of two kinds of domains of Ga-face and N-face, that is, (0 0 0 1) and (0 0 0 (1) over bar), respectively. From secondary ion mass spectroscopy (SIMS) measurements, the In content of the film grown at 600 degrees C was found to be lower than that grown at 550 degrees C. These facts imply that the occurrence of(0 0 0 1) single polarity for the films grown at 600 degrees C is related to In desorption during growth and/or incorporation of a small amount of In in the films.