Quasi-amorphous Ta-Al films were obtained at the Ta/Al atomic ratio of similar to 1. The properties of quasi-amorphous films may be different from the polycrystalline ones. In this paper, the Ta-Al-N thin films were prepared by the nitridation of quasi-amorphous Ta-Al alloys using reactive magnetron cosputtering at various nitrogen flow ratios (FN2%=FN2/(FAr+FN2)100%). The mechanical and electrical properties of the Ta-Al-N thin films were related to the quasi-amorphous and polycrystalline microstructure. X-ray diffraction evidenced that the quasi-amorphous Ta-Al-N films were formed at 2-7.5 FN2% while the polycrystalline ones were obtained at 10-20 FN2%. The hardness of Ta-Al-N films was between 7.1 and 18.0 GPa by means of nanoindentation. A maximum hardness was found at 7.5 FN2% due to the composite quasi-amorphous microstructure with nanocrystalline grains embedded in an amorphous matrix to enhance the mechanical properties. The resistivity of the polycrystalline Ta-Al-N films was much higher than that of the quasi-amorphous Ta-Al-N. The high resistivity of Ta-Al-N at 10-20 FN2% was about 9130-25,400 mu Omega cm in the nonconducting range.