Microbial nanotechnology is currently helping to address human needs in many areas of life. One of these fields is the production of cellulose nanomaterials, which are used in many medical, agricultural, environmental and industrial applications. In this study, the novel strain Aspergillus nidulans optical density 1 (OD1) was isolated as cellulolytic fungus that has the ability to convert cellulose into nanocellulose through partial degradation under optimized conditions. The optimization conditions include incubation of fungal pellets with the microcrystalline cellulose (MCC) for 4 h at pH 6 with addition of 1 mM of Zn and 2 mM of Mn ions. Furthermore, feedback inhibition for exocellulase and B-glucosidase activity was performed to the concentrated cellulases of A. nidulans in order to prevent the complete degradation of cellulose, hence increasing nanocellulose yield. The better results of enzyme feedback inhibition were obtained due to addition of 1% of cellobiose and 2% glucose for the enzyme/MCC mixture for 4 h. The concentrated A. nidulans cellulases were applied to produce nanocellulose from cotton fibers as well as rice straw as common agricultural cellulosic materials and wastes. According to Transmission electron microscope (TEM) and particle size distribution, the average particle sizes of nanocellulose were (9–20) nm and (2–17) nm for cotton fibers and rice straw wastes, respectively. The obtained results revealed that nanocellulose can be biosynthesized using fungal cellulases produced under optimized conditions using cellulosic materials available as agricultural wastes. Further investigation of the produced cellulose nanomaterials can be conducted to demonstrate its compatibility with various medical, environmental, and industrial applications.