Abstract: Three Mongolian and han cross-bred rams (30±1.82) kg live weight with a permanent cannula in the rumen were used to investigate the effect of elimination of anaerobic fungi on fibre digestibility of straw with nylon bag methods in sacco. The results showed that the degradation dynamic parameters of different fibre were changed and the degradation rates of DM，NDF, ADF were significantly decreased (P<0.05). Digestibility of NDF, ADF was also significantly decreased (P<0.05), but the degradation rate of DM was no obvious difference. It suggested that the anaerobic fungi chiefly influence the fibre digestion.