The objective of this study was to examine if polysaccharides from Cassiae Seeds (PCS) can be used as prebiotics to improve the intestinal microflora of piglets with an in vitro and an in vivo trial. The in vitro trial was conducted to study the dose-response effect of PCS on the growth of E. coli 09 and Lactobacillus with traditional plate count method. The gradient culture mediums, containing 3.2, 1.6, 0.8, 0.4, 0.2, 0.1, 0.05, 0.025 and 0% PCS, were inoculated with E. coli09, Lactobacillus and cecum content, respectively. PCS had no influence on the growth of E. coli09 from rejuvenation fluid, but inhibited the growth of E. coli09 from cecum content when the concentration of PCS was higher than 0.1%. Lactobacillus counts were significantly increased with 0.1% PCS or higher (p< 0.05); and the largest increase was found with 0.8% PCS. With the inoculum of cecum content in the medium, Lactobacillus counts increased when the concentration of PCS was 0.4% and 0.8%, whilst E. coli 09 counts decreased. The in vivo trial was carried out to investigate the effect of PCS on the growth of E. coli 09 and Lactobacillus in piglets. Thirty six barrows (average initial BW = 6.5 kg) were randomly divided into 3 groups with 6 each, fed diets supplemented without or with 0.4% or 0.8% PCS. After 14 days, 3 piglets were slaughtered from each group; digesta samples were collected from the ileum, cecum and colon for detection of E.coli 09 and Lactobacillus with plate count method. Samples of the tissue and content of the cecum were taken for detection of caecal microflora profiles with Denaturing Gradient Gel Electrophoresis (DGGE) technique. The dietary inclusion of PCS increased Lactobacillus counts, but reduced E. coli 09 counts in digesta of ileum, cecum and colon of piglets. The dietary inclusion of 0.8% PCS significantly increased the number of electrophoresis brands of caecal bacterial microflora in mucosa and content of the cecum (p< 0.05). These results confirmed the dynamic change in the intestinal microflora profile with the dietary inclusion of PCS in piglets. Thus, PCS can be used as prebiotics to improve the intestinal microflora.