Silicon carbonitride (SiCN) thin films were deposited on n-type Si (100) and glass substrates by reactive magnetron sputtering of a polycrystalline silicon target in a mixture of argon (Ar), nitrogen (N-2) and acetylene (C2H2). The properties of the films were characterized by scanning electron microscope with an energy dispersive spectrometer, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry and ultraviolet-visible spectrophotometer. The results show that the C2H2 flow rate plays an important role in the composition, structural and optical properties of the films. The films have an even surface and an amorphous structure. With the increase of C2H2 flow rate, the C content gradually increases while Si and N contents have a tendency to decrease in the SiCN films, and the optical band gap of the films monotonically decreases. The main bonds are Si-O, N-H-n, C-C, C-N, Si-N, Si-C and Si-H in the SiCN films while the chemical bonding network of Si-O, C-C, C-O, C-N, N-Si and C=N is formed in the surface of the SiCN films. (C) 2010 Elsevier B. V. All rights reserved.