The feasibility of laser spectroscopic isotopic composition measurements of atmospheric N 2 O was demonstrated, although making them useful will require further improvements. The system relies on a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser source emitting wavelength of around 4.6μm, where strong fundamental absorption bands occur for the considered specie and its isotopomers. The analysis technique is based on wavelength modulation spectroscopy with second-harmonic detection and the combination of long-path absorption cell. Primary laboratory tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of 15 N/ 14 N and 18 O/ 16 O isotope ratios. The experiment results showed that the site-selective 15 N/ 14 N ratio can be measured with a precision of 3‰ with 90s averaging time using natural-abundance N 2 O sample of 12.7ppm.