Abstract: In order to conduct the effect of inulin on the performance, pH and the populations of Escherichia coli,Lactobacillus,Bifidobacterium and total bacteria in the digestive tracts and feces in the weaning piglets, 90 28-day-old weaned piglets were randomly assigned to five diets containing antibiotics (Ⅰ)，0.5% inulin＋antibiotics (Ⅱ),1% inulin＋antibiotics (Ⅲ),1.5% inulin＋antibiotics (Ⅳ) and 1% inulin (Ⅴ) with three repeats in each treatment and six piglets in each repeat for 28d, respectively. When the feeding ended, the samples of instestinal content and feces were collected from the piglets fed the diets Ⅰ,Ⅲ,Ⅴ to measure pH and Escherichia coli,Lactobacillus,Bifidobacterium and total bacteria by 16S rDNA PCR method. The results showed that pH in caecum, colon, rectum decreased significantly (P＜0.05), the populations of Lactobacillus in caecum and Bifidobacterium in ileum, caecum, rectum increased when the piglets were fed the diet containing 1% inulin. No consistent effects of inulin were found on the performance and frequency of diarrhea in the piglets. There was a trend to have better performance in the piglets fed the diet containing 1% inulin +antibiotics than containing 1% inulin by itself.