This study aims to experimentally characterize the carbonaceous and nitrogenous species, from the flash pyrolysis of millet stalks and polyethylene plastic bags, using the device of the tubular kiln, coupled to two gas analyzers: Analyzer Fourier TransformInfrared (FTIR) and an analyzer Infrared Non-Dispersive (IRND). Gaseous products analyzed are: CH4, C2H2, C2H4, C3H8, C6H6, CO, CO2, NO2, NO, N2O, HCN and NH3. Whatever the temperature of thermal degradation, the pyrolysis shows us that in terms of mass: _ For the millet stalks, the gaseous compounds are formed mainly CO and CO2 to the carbonaceous species, HCN and NH3, for the nitrogenous species analyzed; _ As regards the polyethylene bags, hydrocarbons for carbonaceous species and HCN, NH3 and NO2 for the nitrogenous species, are most abundant. In addition, the results suppose that in our experimental conditions, the hydrocarbon which is involved primarily in the formation of CO is ethylene C2H4. At the end of this characterization, we determined the rate of carbon and nitrogen found in the volatile gas. With millet stalks we have about 45% of volatile carbon and 15% of the nitrogen of fuel that are found in gaseous products. The results obtained with the plastic bags give 68% carbon and 15% nitrogen found in the nitrogenous species analyzed.