Estimation of the nitrogen loss as N2 and NOx from ecosystem is quite important to close the nitrogen budget. However, due to the high spatio-temporal variations of the nitrogen dynamics in soils does not allow us to investigate the production/consumption processes of these gaseous forms of nitrogen. Although natural abundance of stable isotope is considered to be able to use for the investigation of the N dynamics with respect to gaseous nitrogen losses, nitrogen isotopic measurement of NOx is quite difficult due to its high reactivity. Here we present our preliminary work on the nitrogen isotopic measurement of NOx gas with the filter-pack method (Watanabe et al. 2006) together with the denitrification method (Sigman et al. 2001). NO gas produced from NaNO2 with known nitrogen isotopic ratio via several chemical treatments, then the trapped NO as NO2- and NO3- ions were converted to N2O with denitirifer, then nitrogen isotopic signature was measured by GC-IRMS. We found that the filter-pack method can be applied for the nitrogen isotopic measurement. We applied this method to measure nitrogen isotopic signature of atmospheric NOx and present these data in the poster.