A N2 direct current discharge was studied by optical emission spectroscopy. Experimental parameters as gas flow rate (Q), pressure (p) and current (I) were varied independently, covering the following range: 10 < I < 75 mA, 100 < Q < 1000 sccm and 1.7 < p < 10 torr, corresponding to the following plasma parameters: electron density in the range 109−1012 cm−3 and reduced electric field between 3×10−16 and 10−15 V cm−2. The N2(C $^{3}{\rm \Pi} _{\rm u},\,v'$), N2(X $^{1}{\rm \Sigma} ^{+}_{\rm g}, \,v$) vibrational temperatures and the gas temperature were obtained from the first and second positive systems emissions. The N2(C $^{3}{\rm \Pi} _{\rm u},\,v'$) vibrational distributions did not exhibit a Boltzmann character. A linearization process was employed to such distributions allowing us to calculate the N2(C $^{3}{\rm \Pi} _{\rm u},\,v'$) temperature. The N2(X $^{1}{\rm \Sigma} ^{+}_{\rm g},\,v$) temperature was calculated from the N2(C $^{3}{\rm \Pi} _{\rm u},\,v'$) one on the basis of the Franck-Condon factors. Results and the method of vibrational temperature calculus are presented.