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 lignocellu losic materials.