A balanced gastrointestinal microbial ecosystem is crucial for the health and growth of animals.In the gastrointestinal tract (GIT) of ruminants, cellulolytic bacteria aid in the digestion and absorption of nutrients.Rumen contents and feces in ruminants are often used to assess gastrointestinal microbial communities;however, these sites do not guarantee to represent the diversity of microbes found in the entire GIT.In this study, we investigated the microbiota along the GIT of five Chinese Mongolian sheep using PCR-denaturing gradient gel electrophoresis (DGGE) and real-time PCR analysis.Results indicated that microbiota were more abundant in the stomach and large intestine than in the small intestine.DGGE and real-time PCR revealed the predominance of Firmicutes and Bacteroidetes in the GIT.Meanwhile, Ruminococcus flavefaciens and Clostridium cluster Ⅳ showed significant difference in their abundance along the GIT (P<0.05).Fibrobacter succinogenes was the most dominant species, followed by Ruminococcus albus and R.flavefaciens.The ileum harbored a larger number of cellulolytic bacteria, particlarly-Clostridium cluster Ⅳ, than reported previously.In addition, comparisons between microbiota in the rumen and rectum indicated similar number of total bacteria, Firmicutes, Bacteroidetes, F.succinogenes, Butyrivibrio fibrisolvens, Clostridium cluster Ⅳ,and Clostridium cluster ⅩⅣa, whereas the number of R.albus and R.flavefaciens was higher in the rumen.This study investigated the composition and quantification of GIT microbial community in Chinese Mongolian sheep, and revealed for the first time the cellulolytic bacterial community in these sheep.