A high cellulase-producing fungus was isolated from agricultural waste compost, purified, identified genetically as Aspergillus fumigatus NRCF-122 (accession no. MT318341), and improved by UV-irradiation for cellulase production (named as A. fumigatus mutant-17). Optimal cellulase production conditions were studied using sugar beet pulp “SBP" as the substrate of solid-state fermentation "SSF" technique. The optimal conditions were: initial moisture content ratio (1:2 w/v), incubation temperature (30°C), initial pH of solid culture (10), incubation period (4 days), aeration area (1:100 ratio ((1%)), SBP substrate weight : flask volume of moistened SBP in a 250 mL Erlenmeyer flask, fungal inoculum (seeding) culture age (3 days) and inoculum size (20%, v/w). Studies were also involved the effect of different nitrogen sources where urea is the best nitrogen source for cellulase production. Concerning the application of bioethanol production from yeast, using rice straw cellulose as a source of fermentable reducing sugars), the lingo-cellulosic waste rice straw was first pretreated (with NaOH 1.5%) to reduce crystallinity of cellulose & removing lignin and other inhibitors, enhancing the subsequent process (saccharification) of rice straw cellulose. Then, its cellulose was saccharified enzymatically by cellulases (produced from SBP as substrate (under SSF condition) as substrate under the optimum conditions) resulting in reducing sugars. one of the largest livestock production operating costs is the feed bill. In our study we evaluated the resulted crude protein content of the fermented SBP and the results declared that, the total digest nutrient (TDN) and gross energy performance were increased, where as crude fiber, acid detergent fiber ADF & neutral detergent fiber NDF were decreased, thereby upgrading the feed quality of biologically treated SBP.