The present research aims to study the possibility of generating heat energy from four common Egyptian, agricultural wastes (rice straw, corn stovers, cotton stalks, and sawdust) through thermal decomposition technology in order to select the best residues that can be used as feedstock for the pyrolysis reactors. The generating of heat energy from the four deduced agricultural wastes was experimentally investigated in a pyrolysis reactor designed in the workshop of the Agricultural Engineering Department faculty of AgriculturalMansouraUniversity. Meanwhile, a series of experiments have been performed to explore the effects of biomass particle size and the provided air quantity on gas composition and gas yields of the thermochemical decomposition of the four deduced agricultural wastes.The influences of biomass particle sizes and the provided air quantities on the compounds existing in exhaust gasses obtained from the four tested agricultural wastes samples were examined in relation to the yield and composition of the gasses product. The gasses products were measured and analyzed by a gas analyzer. Whereas, the emission rates of CH4, CO2, and O2 produced from each waste samples were described by means of exhaust gasses percentages. The obtained results indicated in general that the CH4 percentages emitted from the four tested residues were highly dependent on residue lengths and provided amount of fresh air. Whereas, the highest CH4 percentages were 72.6, 77.5, 79.2 and 76.2%) for the thermal decomposition pressing of rice straw, corn stovers, cotton stalks, and sawdust respectively. These maximum CH4 percentages were accomplished residue lengths of 15 cm and zero provided amount of fresh air. The CO2 maximum percentages were 28.1, 25.2, 25.0 and 25.3 % respectively. These percentages were accomplished residue lengths of 20 cm and 0.006 m3/min provided amount of fresh air. The corresponding O2 maximum percentages were 0.56, 0.53, 0.51 and 0.5.