From the viewpoint of hardness, chemical bonding states of nitrogen-doped hydrogenated amorphous carbon film were characterized by Ultra violet (UV) Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. UV Raman spectra revealed that disorder of the structure in nitrogen-doped hydrogenated amorphous carbon was promoted by applying higher bias voltages in the preparation. FT-IR spectra showed that N-H bonds decreased and sp(3)C-sp(3)N bonds increased with the increase of the bias voltages. The content of sp(3)C-sp(3)N bonds was maximized at the bias voltage of -800 V We found out a guarantee that the content of sp(3)C-sp(3)N bonds against bias voltages correlated with the hardness obtained by nanoindentation test. The structural disorder and the increase of sp(3)C-sp(3)N bonds are possible source of the hardness in the case of nitrogen-doped hydrogenated amorphous carbon. (C) 2003 Elsevier B.V. All rights reserved.