The influence of GaN buffer layer on crystallinity of indium nitride layers grown on (1 1 1)GaAs was investigated. The InN layers were grown at 100°C on the GaN buffer layer with various growth temperatures and thicknesses. It was found that both the growth temperature and thickness of GaN buffer layer are critical for obtaining single-crystalline InN on (1 1 1)GaAs substrates. A single-crystal GaN buffer layer with thickness of about 30 nm was needed to obtain high-quality InN epilayers on (1 1 1)GaAs substrates in our case.