Several nc-TiN/a-TiB2 thin films comprised of nanocrystalline (nc-) TiN and amor phous (a-) TiB2 phases were deposited on Si(100) at room temperature by reactive unbalanced dc magnetron sputtering, followed by vacuum annealed at 400, 600, 80 0 and 1000℃ for 1h, respectively. Effects of B content on microstructure, mecha nical behaviors and thermal microstructure stability have been investigated by X -ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and nanoindentation measurements. The results indicated that B addition greatly affected both microstructure and mechanical behavior of nc-Ti N/a-TiB2 thin films. With increasing B content the grain size decreased. A maxim um hardness value of about 33GPa was obtained at B content of about 19at.%. The improved mechanical properties of nc-TiN/a-TiB2 films with the addition of B int o TiN were attributed to their densified microstructure with development of fine grain size. Only addition of sufficient B could restrain grain growth during an nealing. High B content resulted in high microstructure stability. The crystalli zation of amorphous matrix occurred at about 800℃, forming TiB or TiB2 crystall ite, depending on B content. Before that no change in bonding configuration was found. Several nc-TiN / a-TiB2 thin films comprised of nanocrystalline (nc-) TiN and amor phous (a-) TiB2 phases were deposited on Si (100) at room temperature by reactive unbalanced dc magnetron sputtering, followed by vacuum annealed at 400 , 600, 80 0 and 1000 ° C for 1 h, respectively. Effects of B content on microstructure, mecha nical behaviors and thermal microstructure stability have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron Spectroscopy (XPS) and nanoindentation measurements. The results indicated that B addition greatly affected both microstructure and mechanical behavior of nc-Ti N / a-TiB2 thin films. With increasing B content the grain size decreased. A maxim um hardness value of about 33 GPa was obtained at B content of about 19 at.%. The improved mechanical properties of nc-TiN / a-TiB2 films with the addition of Binto TiN were attributed to their densified microstructure with development of fine grain size. Only addition of su The Bicrystal B could restrain grain growth during an nealing. High B content resulted in high microstructure stability. The crystalli zation of amorphous matrix occurred at about 800 ° C, forming TiB or TiB2 crystallite, depending on B content. Before that no change in bonding configuration was found.