Abstract: 144 Duroc×Large white×Landrace crossbred piglets weaned at 18 d, weighted 5.6 kg, sorted by weight and gender, were allotted to 6 treatments, with 3 replicates per treatment and 8 piglet per replicate．The basal diet was corn-soybean, without antibiotics or probitotics, which was fed to the 1st group as negative control(CTL)．The 2nd group was fed with basal diets adding chlortetracycline hydrochloride (CTC) in 150 mg/kg as the positive control．The 3rd-5th group were fed with basal diets adding 1 000 mg/kg Bacillus Natto sawamura (Natto) and 1 000 mg/kg or 2 000 mg/kg mannan oligosaccharides(MOS) respectively, the 6th group was fed with basal diets adding 1 000 mg/kg MOS and 500 mg/kg Natto．Intestinal pH, colonic gut flora population were examined, and the intestinal morphology were detected．The results were as follows: Dietary Natto and MOS supplementation have a trend of reducing pH value of jejunum, ileum, caecum and colon cotent, the intestinal pH were reduced significantly when Natto used combining with MOS. Dietary Natto increased lactobacillus and bifidobacterium population in colonic content, and lactobacillus population in mucous membrane increased, dietary MOS increased population of lactobacillus both colonic content and mucous membrane, group of 2 g/kg MOS reduced population of E.coli both colonic content and mucous membrane. In colonic content, cooperation of Natto and MOS had a suppressoion to E.coli compared with CTL and an enrichment of lactobacillus compared with CTC group(P<0.05), while in colonic mucous membrane, population of lactobacillus increased and E.coli decreased, with a remarkable difference to CTL and CTC group(P<0.05). Natto increased villus height of mucous membrane, as same as group of cooperation of Natto and MOS , There is no difference between each group for crypt depth of mucous membrane(P>0.05), the ratio of villus height and crypt depth of group Natto, 1 g/kg MOS, and the group of cooperation of Natto and MOS increasing remarkable compared to CTL group.