AlN/BN nanocomposites were fabricated by hot-pressing AlN-BN nanocomposite powders, which are AlN powders partly coated with turbostratic BN (t-BN). The transformation of crystalline phase in synthetic process of the nanocomposite was investigated by X-ray diffractometer (XRD). In addition to fracture strength, Young's modulus and machinability, thermal conductivity of the nanocomposites was measured, and they were compared with those of conventional AlN/BN microcomposites and monolithic AlN.