The chemical modification of sugarcane bagasse with succinic anhydride using pyridine as solvent after ultrasound irradiation was studied. The optimized parameters included ultrasound irradiating time 0-50 min, reaction time 30-120 min, succinic anhydride concentration by the ratio of dried sugarcane bagasse to succinic anhydride from 1:0.25 to 1:1.50, and reaction temperature 75-115 degrees C are required in the process. The extent of succinoylation was measured by the weight percent gain (WPG), which increased with increments of reaction time, succinic anhydride concentration, and reaction temperature. The ultrasound irradiation has a positive effect on bagasse succinoylation process. On the other hand, the ultrasonic pre-treatment application broke down the cell wall polymers, resulting in, therefore, a negative effect on the WPG. Evidences of succinoylation were also provided by FT-IR and CP MAS (13)C NMR and the results showed that the succinoylation at C-2 and C-3 occurred. The thermal stability of the succinylated bagasse decreased upon chemical modification.