Noisy and spectrally not well resolved molecular emission spectra of the 306.357nm OR band were employed for evaluation of the rotational temperature in different plasma sources, in the temperature range from 300K to 6000K, when an apparatus function of a recording system is unknown. The method, is based on a comparison of experimental data with a theoretical spectrum. Different weakly ionized plasma sources are examined. Temperatures, obtained from the OR spectra, are in good agreement with temperatures obtained by using others techniques. Thus, the OH spectra are very useful for temperature measurements of non-equilibrium plasmas.