Indium nitride (InN) films were grown on (111)GaAs substrates by reactive magnetron sputtering using an indium target. It was found that the crystal quality of LnN films depends strongly on the substrate temperature and sputtering gas pressure, and highly c-axis preferred wurtzite InN films can be obtained at growth temperature as low as 100 degreesC. Based on these results, the growth mechanism of LnN films in the reactive magnetron sputtering was discussed.