The role of added inorganic salt on the thermal degradation of lignin was studied The results were compared with the thermal analyses of two types of agricultural residues: rice straw with high silica content and bagasse with low silica. Compared to wood, thermal decomposition of such materials is faster, with a dual mechanism concept similar to wood. In general, the activation energy for rice straw is about 19.3 Kcal/mol while that of bagasse is 33.4 Kcal/mol. This proves that inorganic material either inherited or added changed the thermal activities of the lignocellulosic materials.