In this paper, nanostructured tin oxide doped with Nitrogen was investigated by first principle calculations. At first, band structure, density of states, and projected density of states were evaluated for pure tin oxide. Then, the effect of doping with Nitrogen was studied for cases when N replaces O atom, Sn atom, respectively, and in two interstitials situation. Results were compared with pure reference case. Except of one interstitial case, Nitrogen doping usually plays the role of a p-type doping, however the decrease of band gap occurs in all cases. [ABSTRACT FROM AUTHOR]