A trace level of N2 and Ar gases in O2 ambience were quantitatively analyzed for the first time by glow discharge optical emission spectroscopy. Microplasma was generated in a compact gas cell by a metal (Au) electrode pair of 1 mm diameter and ∼1 mm separation with the driving voltage of ∼0.9 kV and the current of ∼5 mA in ∼60 Torr. 358 and 813 nm optical emission bands were used for N2 and Ar detection, respectively. A spectroscopy fiber bundle having a circular input cross section of ∼700 µm in diameter and an output of 100 µm in width and 3 mm in height was employed to promote the signal collection efficiency while preserving high spectral resolution. As a result, the detection sensitivities <1 ppm (3 - σ) were attained for both N2 and Ar within 10 s. The detection accuracy was also promoted by correcting the N2 and Ar band signal intensities using the neighboring O emission band intensities, which led to detection errors <2% (3 - σ) for both N2 and Ar.