We report on the preparation of boron carbon nitride (BCN) thin films by pulsed laser ablation of a sintered B4C target and the compositional and structural characterization of the films. The film preparation was performed with assistance of nitrogen ion beam from a Kaufman source. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used for compositional analysis and structural characterization. The results showed that the prepared films contain several chemical bonds such as B-N and C-N. The BCN films were found to show good adhesion to the substrates and have a high transparency from visible to near-infrared region. WE also grew films in nitrogen background without ion beam assistance and in vacuum. The atomic ratio of boron, carbon and nitrogen and the chemical bonds are strongly dependent on the deposition conditions. The ion beam assistance, i.e. the reactive nitrogen environment and the bombardment of the growing films by the energetic species in the nitrogen ion beam, is beneficial to the incorporation of nitrogen.