Gellulases are important hydrolytic enzymes. Gellulases are widely used in the food, feed, textile, pulp and paper industries. Microbial conversion of cellulosicllignocellulosic biomass into useful products is a complex process involving combined action of three enzymes namely endoglucanase (EG 3.2.1.4), exoglucanase (EG 3.2.1.91) and beta-glucosidase (EG 3.2.1.21). In this study 15 decay wood samples of some tropical forest in the North of Vietnam had been screening for fungi with cellulase activity. 49 strains were isolated, 11 selected strains with largest clear zone (D-d 10mm) were further quantitatively assayed for cellulase activities when culturing in Gzapek medium with GMG as carbon source. Maximum cellulase activity was exhibited by SBC 5-6 (0. 14U/ml). Morphological and bio-molecular method were used to identify SBC 5-6 as Aspergillus fumigatus.