[Objective] The aim of this study is to understand the population composition of methanogens in rumen fluid of grazing Inner Mongolian cashmere goat. [Method] Total DNAs of various bacteria in rumen fluid were isolated for PCR amplification using the specifically designed primers based on conservative mcrA sequence of methanogens; then mcrA specific clone library was accordingly established. The restriction fragment length polymorphism(RFLP) of the library was further analyzed by digestion of restriction enzyme Taq I. [Result] One hundred and five randomly selected specific colonies were classified into six RFLP types, among which the dominant type accounts for 38%, and other types account for 27%, 18%, 5.5% and 4.5%, respectively. [Conclusion] There are at least six different methanogens in rumen fluid of grazing Inner Mongolian cashmere goat.