Nanocrystalline aluminium titanium nitride (AlTi3N) thin films were deposited on Si (100) wafers and grids by reactive magnetron co-sputtering technique using titanium and aluminium targets. The films were sputtered in Ar and N2 mixture at a constant flow rate under different conditions of deposition time ranging from 15 to 60 minutes. The crystal structure was characterized by X-Ray diffraction (XRD) and microstructure was analyzed by transmission electron microscopy (TEM). The results indicated that the formation of polycrystalline AlTi3N with the orthorhombic structure and the development of crystal structure was observed by varied the deposition time. The microstructure of films was good according to the XRD results. On the other hand, after annealed the films at 500OC in the air for 1 hour, the crystal structure did not change that exposed the stable structure of AlTi3N films.