Acetic acid was used to pretreat and fractionate wheat straw. A 25% acetic acid solution at 160 degrees C could remove all xylan and 26.2% of lignin in the wheat straw at a 10% solid concentration while recovering 94.2% of glucan. The glucan content of the pretreated wheat straw was 60.9% compared to 35.5% in the raw wheat straw. After the 6-day hydrolysis with a cellulase at a load of 15 FPU/g glucan, 67.6% of the glucan in the acetic acid-pretreated wheat straw was hydrolyzed into glucose, compared to 58.3, 26.0, and 24.4% for pure cellulose, wheat straw pretreated with hot water at 160 degrees C, and raw wheat straw, respectively.