Abstract: The aim of the study was to investigate the effect of diets with different crude fiber levels on xylanase activity of microorganism in donkey caecum. The conventional diet group, high-fiber diet group and high-starch diet group were included in this study. The xylanase activity of microorganism of different groups were determined and statistically analyzed. The results showed that the xylanase activity of cecal microorganism of high-fiber diet group and high-starch diet group were significantly higher than that of the conventional diet group （P〈0.05）.