In this work, transmission Fourier transform infrared spectroscopy (FTIR) has been used to study the native oxides on the nitrogen doped tetrahedral amorphous carbon (ta-C:N) thin films deposited by a filtered cathodic vacuum arc system, and the reactions of the oxides with 0.1M NaOH aqueous solution. The native oxides on ta-C:N films possess the bonds of C=O and C―O, and dissociation bond of –OH as on other carbon materials. The amount of the oxides containing C=O and C―O bonds increases with the sp 2 C fraction inside the material. The oxides can react with 0.1M NaOH solution effectively to produce soluble salts, and the N―C groups in the films become active for oxygen absorption to produce N=C=O after the reactions. When the applied electrode potential is more negative than a critical negative value, the native oxides increase the electrochemical activity of ta-C:N film electrodes in aqueous sulfuric acid solution.