Abstract: Hemicellulose was extracted from corncob and further modified by acetylation. Ultrasonic-assisted alkali method was employed for the extraction, in which sulfuric acid (H₂SO₄) and elemental iodine (I₂) were used as co-catalyst for the acetylation of hemicellulose, respectively. Corncob hemicellulose and its acetylated products were characterized by infrared spectroscopy (IR), thermogravimetric analysis (TGA) and nuclear magnetic resonance (NMR). The yield and extraction rate of corncob hemicellulose were 33.7% and 81.0%, and the hemicellulose content reached 85.3wt%. The acetylation of corncob hemicellulose gave 84.6% yield and 1.27 degree of substitution (DS), respectively. The separation of hemicellulose from corncob using alkali method was effectively shortened by ultrasonic assistance, and the yield and extraction rate of corncob hemicellulose were improved. Concentrated sulfuric acid (H₂SO₄) and elemental iodine (I₂) were effective co-catalyst for the acetylation of corncob hemicellulose. The results of IR and NMR showed that hemicelluloses were acetylated successfully, and TGA revealed that the thermal stability of the acetylated hemicellulose was improved. Moreover, the DS value of the acetylated product was moderate. Therefore, the acetylated product is expected to be used to prepare biodegradable materials for food packaging.