Cellulosic compounds in manure limit the hydrolysis step in energy production from animal waste under anaerobic conditions. Because anaerobic fungi produce plant carbohydrate hydrolysing, cellulolytic, hemicellulolytic, glycolytic, and proteolytic enzymes, they are considerably important for the biodegradation of animal manure. In this study, we examined the effects of bioaugmentation of anaerobic rumen fungi in various ratios of inoculums on biogas production of anaerobic digesters fed with animal manure. The highest biogas production was observed in the R-2 (15%) digester with a rate of 5500 mL/d, almost 60% of total biogas, due to addition of anaerobic rumen fungi. In addition, changes in the microbial community structure were detected by next-generation sequencing. It was also proven that anaerobic rumen fungi are more effective on Lentisphaerae, Clostridium, and Methanolinea sp. in terms of the highest biogas production. Based on our results, anaerobic rumen fungi appear to be a promising alternative for improving biogas production from different types of lignocellulosic compounds due to their non-specific extracellular ligninolytic enzymatic system. (C) 2017 Elsevier Ltd. All rights reserved.