We have prepared indium nitride (InN) thin films on glass and (0001) alpha-Al2O3 substrates by rf reactive magnetron sputtering and studied their growth and nanostructure using analytical techniques such as X-ray diffraction (XRD), reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). The growth and nanostructure are strongly affected by the He addition to the Ar-N-2 sputtering gas mixture. The c-axis preferentially oriented structure is formed by the He addition. This effect of the He addition occurs similarly both for glass and for(0001) alpha-Al2O3 substrates.