Abstract: Three levels of mixture of cellulase and xylanase supplementations (0, 10.0 and 50.0 mg, respectively) and two pretreatment time (0 and 24 h) in triplicate were used to determine the effects of the mixture enzyme on the enzyme activities and fermentation characteristic of Chinese wildrye by mixed ruminal microorganisms in vitro. Fibrolytic enzymes increased (P<0.05) activities of xylanase and endoglucanase at 0 and 8 h and exoglucanase activity at 0 h postincubation in fermentation fluid. In addition, the enzyme activities increased with exogenous enzyme preparation level. However, the exogenous enzyme preparation did not affect the enzyme activities at 24 and 48 h of incubation. The content of acetic acid at 24 and 48 h, the total volatile fatty acids content at 8, 24, 48 h incubation and the cumulative gas production at end of incubation were increased (P<0.05) by the enzyme treatment. Exogenous enzyme had no effects the concentrations of valeric acid and isovaleric acid during incubation (P>0.05). The results suggested that the exogenous fibrolytic enzymes enhanced the activities of xylanase, endoglucanase and exoglucanase in the fermentation fluid in early incubation, finally increased total volatile fatty acids output and improved rumainal fermentation characteristic in vitro.