Abstract: In order to determine the ferment properties and bifidogenic action of inulin, an in vitro fermentation experiment was conducted to anaerobically incubate fresh feces of growing pigs with inulin (0, 1, 2, 4, 6, 8 g/L, respectively) for 24 h at 37℃, and then determine pH and the populations of Escherichia coli, Lactobacillus, Bifidobacterium and total bacteria in the culture medium. The results showed that pH and the number of Escherichia coli linearly decreased (P<0.001),and the number of Lactobacillus, Bifidobacterium and total bacteria in the culture medium linearly increased (P<0.01 or P＝0.059). It was concluded that there were dosageresponse relationships between inulin additive level and bacteria (Escherichia coli, Lactobacillus, Bifidobacterium and total bacteria) amount or pH in the culture medium.