【Objective】 A new method for homogeneous modification of agricultural and forest residues at room temperature was proposed.【Method】 Homogeneous derivatization of sugarcane bagasse with isobutyric anhydride in the dimethyl sulfoxide/ 1-methylimidazole (DMSO/NMI) solvent system was investigated at room temperature in the present study.【Result and conclusion】 Holding reaction time for 180 min, the mass percent gain (WPG) of sugarcane bagasse increased from 10.3% to 49.2% with the increment of the mass ratio of isobutyric anhydride to ball-milled sugarcane bagasse from 1∶1 to 6∶1. The increase of reaction time from 15 min to 45 min resulted in an enhancement of WPG from 25.1% to 27.4%, keeping the mass ratio of isobutyric anhydride to ball-milled sugarcane bagasse at 3∶1. However, further improvement of reaction time led to a decrease in WPG, and the WPG decreased to 24.7% within 240 min under the given conditions. FT-IR and CP/MAS ¹³C-NMR analyses indicated that the esterification between sugarcane bagasse and isobutyric anhydride did occur at room temperature in DMSO/NMI. The esterification of carbohydrates and lignin with isobutyric anhydride were both confirmed.