Aims:The findings of this research are the conversion of the cotton fiber wastes from the textile mills into the valuable product as ethanol using fungal cellulases. Methodology and results: Samples of cotton fiber waste were collected from different localities at Giza Spinning and Weaving Company. Twenty-five fungal isolates were found to exhibit growth on the static basal salt medium at pH 5, containing cellulose as the only carbon source. Ten isolates showed cellulase activities when assayed on different substrates in the reaction mixture to detect their ability to produce cellulase enzymes as carboxy-methyl-cellulase (CMCase), avecillase and cellobiase. The genera Aspergillus was detected by microscopic slide examination of spores and mycelium. Molecular analysis of the most potent strains were designed as Aspergillus foetidus strain NRC4s (MH553343) for endoglucanase production and Aspergillus niger strain NRC6S (MH553376) for exoglucanase and betaglucosidase production. They were grown separately on cotton fibers waste sterilized medium for five days. The resultant hydrolyzates were mixed, sterilized and used as a medium for ethanol production under anaerobic conditions at 30 °C by suitable yeast strain Saccharomyces cerevisiae NRC 514. The produced ethanol was 1.5 mL ethanol/L after 24 h incubation time. Conclusion, significance and impact of study: Egypt has a vast number of textile mills. So, the objective of treating lignocellulosic biomass to synthesize biofuels was essential. This research finding indicates the potential of using bioconversion of cotton fibers wastes to ethanol by fungal cellulases. However, further studies are required to take it further.