Rice straw was divided into fractions by morphological character, and the enzymatic hydrolysis of these fractions was investigated. Chemical composition and the proportions of cells of different compositions were very variable in different fractions. This has a fundamental effect on the enzyme adsorption capability and hydrolysis performance. Cellulose and hemicellulose contents affected hydrolysis performance positively, silica and lignin in the rice straw had a negative effect. Morphological separation appears to be necessary if rice straw fractions are to be useful as carbohydrate sources. (c) 2005 Elsevier Ltd. All rights reserved.