Background: Cellulose is the most abundant biomass on earth. The major players in cellulose degradation in nature are cellulases produced by microorganisms. Aerobic filamentous fungi are the main sources of commercial cellulase. Trichoderma reesei has been explored extensively for cellulase production; however, its major limitations are its low β-glucosidase activity and inefficiency in biomass degradation. The aim of this work was to isolate new fungal strains from subtropical and tropical forests in China, which produce high levels of cellulase in order to facilitate development of improved commercial cellulases.