To enzymatically hydrolyze cellulose of rice straw to glucose, the effect of pretreatment of rice straw with 15 strains of basidiomycetes is evaluated in terms of the quantitative changes in the components of pretreated rice straw and their susceptibility to enzymatic hydrolysis. Pleurotus ostreatus was found to be one of the most suitable white-rot fungi for biological pretreatment of rice straw. Of 11 strains of P. ostreatus tested, ATCC 66376 was found to have the properties superior to the other strains. Thus, in the pretreatment for 48 d, P. ostreatus ATCC 66376 degraded 39% Klason lignin and retained 79% cellulose in the pretreated rice straw. When the rice straw pretreated with this fungus was hydrolyzed with a commercial cellulase, the net yield of glucose determined on the basis of the weight of cellulose fraction of the untreated rice straw was the highest.