Nitrogen doped Diamond-like carbon thin films were deposited on n-Si and SiO2 substrates by rf magnetron sputtering using pure graphite (99.999%) as the target material and mixtures of Ar, N-2 and H-2 for plasma generation. The dependence of structural and optical properties on nitrogen content was investigated using XPS, Raman spectroscopy, FT-IR spectroscopy, and Ellipsometry studies. It was found that as the nitrogen content was increased in the plasma, sp(2) bonding favored. Also it was observed that oxygen contamination increased with nitrogen content. Typical C-H stretching modes connected with diamond-like carbon could be seen in FT-IR spectra. The D and G bands were well defined and it was observed that as nitrogen content increased G band was enhanced. Ellipsometry studies revealed that the optical constants like refractive index (n) and extinction co-efficient (k) increased with increase in nitrogen content as well as substrate temperature.