Tiny variation in natural abundance ratios of stable isotopes of nitrogen and oxygen in nitrous oxide (N₂O) can be used as a fingerprint of this trace gas that causes greenhouse effect and stratospheric ozone depletion. Toward the understanding of the global budget of N₂O and its temporal change, we developed an automated sample preparation system that can be used to measure the stable isotope ratios in N₂O in various air samples collected into flasks with high precision and less labor.