An aquatic weed biomass, Eicchornia crassipes, present in abundance and leading to a threatening level of water pollution was used as substrate for cellulase and beta -glucosidase production using wild-type strain Aspergillus niger RK3 that was isolated from decomposing substrate. Alkali treatment of the biomass (10%) resulted in a 60-66% increase in endoglucanase, exoglucanase, and beta -glucosidase production by the A. niger RK3 strain in semisolid-state fermentation. Similarly, the alkali-treated biomass led to a 45-54% increase in endo- and exoglucanase and a higher (98%) increase in beta -glucosidase production by Trichoderma reesei MTCC164 under similar conditions. However, the cocultivation of A. niger RK3 and T. reesei MTCC164 at a ratio of 3:1 showed a 20-24% increase in endo- and exoglucanase activities and about a 13% increase in the beta -glucosidase activity over the maximum enzymatic activities observed under single culture conditions. Multistep physical (ultraviolet) and chemical (N-methyl-N'-nitrosoguanidine, sodium azide, colchicine) mutagenesis of the A. niger RK3 strain resulted in a highly cellulolytic mutant, UNSC-442, having an increase of 136, 138, and 96% in endoglucanase, exoglucanase, and beta -glucosidase, activity, respectively. The cocultivation of mutant UNSC-442 along with T. reesei MTCC164 (at a ratio of 3:1) showed a further 10-11% increase in endo- and exoglucanase activities and a 29% increase in beta -glucosidase activity in semi-solid-state fermentation.