Objective To investigate the effects of Saccharomyces boulardii ( S. boulardii) on the col-onization of Helicobacter suis ( H. suis) in stomach and the formation of gastric mucosa associated lymphoid tissue (MALT) during H. suis infection. Methods Sixty C57BL/6 wild type mice were randomly divided into six groups. The mice in group A and group B were respectively given sterile distilled water and S. boulardii twice by gavage and then infected with H. suis for one week. The mice in group C and group E were given sterile phos-phate buffer saline by gavage for one week and then respectively given sterile distilled water and S. boulardii by gavage twice a week for 12 weeks. The mice in group D and group F were infected with H. suis for one week and then respectively given sterile distilled water and S. boulardii by gavage twice a week for 12 weeks. Serum and gastric tissue samples were collected from each mouse. Results The bacterial loads of H. suis in the stomachs of mice in group B were significantly lower than those in group A. No significant differences in the levels of se-creted IgA( sIgA) in serum and gastric tissue samples and the expression of IFN-γat mRNA level in gastric mu-cosa samples were found between the two groups. The expression of H. suis 16S RNA and the formation of gastric lymphoid follicles were detected in mice in groups D and F. The levels of sIgA in serum and gastric tissue sam-ples and the expression of IFN-γ and CXCL13 at mRNA level in gastric mucosa samples increased significantly in groups D and F as compared with groups C and E. Compared with the mice in group D, the bacterial loads of H. suis in stomachs, the numbers of MALT per unit length of gastric mucosa and the expression of IFN-γ and CXCL13 at mRNA level in gastric mucosa decreased significantly in mice from group F, but the levels of sIgA in serum and gastric tissue samples increased significantly. Conclusion S. boulardii could inhibit the colonization of H. suis in stomach and suppress the formation of gastric MALT during H. suis infection.