Abstract: Background and Objective: Cellulase as a fibrolytic enzyme is a highly effective tool for agricultural waste treatments. Production of cellulase enzyme on medium of agricultural wastes by Fusarium graminearum to be used in ruminant feeding was the main objective of this study. Materials and Methods: Impact of initial pH of growth medium, different nitrogen sources and variety of agriculture by products as a carbon sources on cellulase production have been studied. Electron microscope was used for investigate the impact of the resultant cellulase on corn stover degradation, while batch culture technique was used for investigate impact of different levels of the produced and commercial cellulases on total mixed ration digestibility by rumen microorganisms (in vitro). Results: Cellulase maximum production by F. graminearum was obtained at 20% corn stover, initial pH of growth medium 5.0 and peptone as a nitrogen source. All addition levels of the produced cellulase increased dry matter (DM), neutral detergent fiber (NDF), acid detergent fiber (ADF), cellulose and hemicellulose degradability of the treated diets, but the maximum produced cellulase efficiency% for dry matter degradability was obtained at 1200 IU kg–1 DM reached 23.19% over the control. Conclusion: Utilization of the produced cellulase in enrichment of the feeding value of the agricultural by-products may help in overcome of the feed gap with good impact on environment and public health.