Drastic changes in the bonding are found in amorphous hydrogenated carbon nitride (a-CNx:H) film as a function of nitrogen concentration (or N/C ratio). The total C-sp 3 fraction and hardness shows a sharp decrease (at N/C=0.40) whereas optical band gap and resistivity shows a gradual increase as nitrogen concentration increases from 0.07 to 0.58. Raman spectrum of a-CNx:H film is fitted with both Gaussian (integrated intensity ratios are used instead of the height ratios of the Lorentzian (D mode)) and Breit–Wigner–Fano (BWF, G Mode) method for a comparative study of optical properties and crystalline size of the graphite domain. Visible Raman (488nm) spectroscopy finds that the in-plane crystalline size of graphite domains (L a ) is increased (from 34 to 38Å) with nitrogen incorporation. Optical band gap of a-CNx:H solid measured by means of ellipsometry differs from the one obtained from Raman spectroscopy. In addition, we propose a simple extension of the existing band gap model to obtain the optical band gap of a-CNx:H film from Raman spectrum. Our estimation agrees well with the experimental value.