We use hole method to study the antibacterial effect of the chitosan and its derivative on Helicobacter pylori， the results shows that it can not generate antibacterial circle in different concentration of chitosan and carboxymethyl chitosan. Chitosan oligosaccharide B(degree of deacet ylation，DD=94%， 50 mg/mL). has generated the antibacterial circle of Helicobacter pylori， the radius of bacteriostatic ring is (4.1±0.23) mm， while positive control (metronidazole， 10 mg/mL) is (5.5±0.15) mm. Chitosan oligosaccharide B (50 mg/mL) can vividly decrease the biological mass of Helicobacter pylori， while the chitosan oligosaccharide A (50 mg/mL) can not influence the growth of strain. Conclusion shows that chitosan oligosaccharide B(50 mg/mL) has the ability to restrain the Helicobacter pylori. The chitosan oligosaccharide A (deacetylation degree of 80%)， chitosan and carboxymethyl chitosan provided in this experiment did not have the effect of inhibiting Helicobacter pylori.