Abstract: Six fibre degrading fungus were isolated from rumen of mithun (Bos frontalis) at National Research Centre on Mithun, Jharnapani, Medziphema, Nagaland using specific media for rumen fungus. These isolated fungal cultures showed higher fibre degrading enzymes like CM cellulase, Xylanase and Avicelase activity. Addition of fungal culture in the mixed rumen liquor of mithun increased in vitro gas production. The identification and characterization of these isolates was done by DNA isolation, Polymerase Chain Reaction (PCR) amplification, sequencing and plotting of phylogenic tree. The result showed that two isolates were homologus to Orpinomyces species and four isolates were homologus to Neocallimastix species. These isolates can have potential to be used as microbial feed additives in ruminants.