Rotational temperature has been used widely as neutral gas temperature measurement in different types of plasmas (electron cyclotron resonance, inductively coupled plasma, helicon, hollow cathode, etc.), and has been assumed to be in equilibrium with translational temperature. The direct experimental comparison of rotational and translational temperature in low-temperature plasmas has not been reported. In this research, optical emission spectroscopy is used to measure the neutral gas rotational temperature, T-rot, from the second-positive band of a nitrogen molecule (380 nm). The results are compared with the Doppler-broadened translational temperature, T-trans, of Ar (750 nm) and He (587 nm), determined with a high-resolution spectrometer at various partial pressures of N-2 in Ar/N-2 and He/N-2 plasmas. The results demonstrated that Trot and Ttrans are in equilibrium in the conditions [10(10)< n(e)(cm(-3))< 5 x 10(12), 1 < T-e(eV)< 5, 1 < p(fill)(mTorr)< 50] of our plasma experiment. (c) 2006 American Vacuum Society.