An experimental observation on stimulated emission of radiation at liquid nitrogen temperature is reported. The paramagnetic material is synthetic ruby with about 0.1% chromium in Al2O3. The pumping frequency lies at X-band range while the signal freqe-ncy is set at S-band. The dependence of saturation factor on pumping power is measured . The negative temperatuve effect on population distribution is observeb with a pumping power about 10-2 Watt. The ratio of population inversion is 0.44.