This paper is about the use of optical emission spectroscopy as a diagnostic tool to determine the gas discharge parameters of a direct current (98% Ar–2% H 2 ) non-thermal microplasma jet, operated at atmospheric pressure. The electrical and optical behaviors were studied to characterize this glow discharge. The microplasma jet was investigated in the normal and abnormal glow regimes, for current ranging from 10 to 130mA, at ~220V of applied voltage for copper cathode. OH (A 2 ∑ + , ν=0→X 2 Π, ν′=0) rotational bands at 306.357nm and also the 603.213nm Ar I line, which is sensitive to van der Waals broadening, were used to determine the gas temperature, which ranges from 550 to 800K. The electron number densities, ranging from 6.0×10 14 to 1.4×10 15 cm −3 , were determined through a careful analysis of the main broadening mechanisms of the H β line. From both 603.213nm and 565.070nm Ar I line broadenings, it was possible to obtain simultaneously electron number density and temperature (~8000K). Excitation temperatures were also measured from two methods: from two Cu I lines and from Boltzmann-plot of 4p–4s and 5p–4s Ar I transitions. By employing H α line, the hydrogen atoms' H temperature was estimated (~18,000K) and found to be surprisingly hotter than the excitation temperature.