A way to bury the rice straw in the soil is the decomposed rice straw internodes to prevent the black cloud which caused high pollution in Cairo every year. The mechanical and physical properties of  straw residues from cereal crops left on the soil are affected by decomposition rate and moisture content during inter-cropping period. In this research, the study was carried out the relationship between physical characteristics and mechanical properties of mature rice straw as a function of decomposition and moisture content. The mechanical properties of rice straw residues such as shearing and  bending stress were evaluated. Physical properties of ground samples such as moisture content, humid, mean diameter, length and thickness of rice straw internodes were determined. The ear internodes had the lowest mass per unit length and the highest density because of its smaller diameter and stem wall thickness. The difference in maximum force and energy required for failures among internodes is due to their mass per unit length and cross-sectional area. The higher Young's modulus and maximum bending stress of the ear internodes found to be due to its higher properties of hemicelluloses. Bending and shear strengths decreased by 70% and 80% respectively with decomposition due to the loss of mass. Rice straw moisture had opposite effects on bending and shearing strengths. The maximum bending stress decreased by 54% and the shear stress increased by 83%. As both decomposition and moisture greatly modify the mechanical properties of straw. These two factors should be taken into account in the management of straw after harvest.