Both infrared absorption (IR) and electron spin resonance (ESR) spectroscopies have been used to investigate the complicated structure of nanocrystalline cubic boron nitride/amorphous hydro-genated boron nitride thin films. The ESR spectra from this material consist of a component with a four-line hyperfine structure and/or a component with a ten-line hyperfine structure superimposed upon a broad central line. The hyperfine structures are associated with defect centers located in the nanocrystalline phase, whereas the broad line is attributed to dangling bonds in the amorphous phase. The IR spectra consist of three lines around 1400 cm−1: the lines at 1263 and 1505 cm−1 originate in a boron-poor amorphous hydrogenated boron nitride region; the line at 1371 cm−1, in a boron-rich amorphous hydrogenated boron nitride region. These results, together with previously reported electron diffraction spectra, suggest the following picture: small (2.5 nm) nanocrys-tallites of cubic boron nitride (about 5% of the material) are imbedded in a mixed amorphous phase. The amorphous region can be approximated by a mixture of boron-rich and boron-poor amorphous hydrogenated boron nitride.