The corrosion behavior of BCN thin films in aqueous solution was investigated. BCN films with different composition were deposited on a platinum plate by magnetron sputtering in the thickness range of 150-280 nm. In order to understand effect of pH of solutions, BC2.4N samples were immersed in 1 M HCl, 1 M NaCl and 1 M NaOH solution at 298 K, respectively. BCN samples with different carbon content were immersed in I M NaOH solutions to investigate the effect of chemical composition on corrosion resistance. The corrosion rate of the samples were measured by ellipsometry. The corrosion rates of B1.0C2.4N1.0 films in the immersion test were NaOH>NaCl>HCl in sequence. With increasing carbon content in BCN films, the corrosion resistance of BCN films is enhanced. The lowest corrosion rate was obtained for B1.0C(3.2-4.4)N1.2 films (C) 2003 Elsevier B.V. All rights reserved.