 Background: Helicobacter pylori infection has been shown to be associated with the development of gastric cancer and peptic ulcer diseases. Eradication of H. pylori infection could reduce the occurence or recurrence of these diseases. However, it was estimated that 15-20 of patients would fail from first line standard eradication therapy and need second line rescue therapy. About 15-30 of patient would fail from second line therapy and need to be rescued with third line therapy. The commonly used salvage regimens include 1 Bismuth based quadruple therapy combined with ranitidine or PPI plus two antibiotics 2 Levofloxacin or moxifloxacin or rifabutin based triple therapy. However, Bismuth is not available in many countries and the administration method is complex. Its usage is limited by the high pill number and low compliance rate. In recent years, the concept of sequential therapy has been advocated in the treatment of H. pylori infection. The regimen includes a PPI plus amoxicillin for five days, followed by a PPI plus clarithromycin and metronidazole for another five days. The eradication rate in the first line treatment of sequential therapy had been reported to be as high as 90. More importantly, it has been demonstrated that the eradication rate among patients with clarithromycin-resistant strains could be as high as 89. According to the Maastricht III consensus meeting, it was recommended that susceptibility test should be done for patients who failed two treatments. Therefore, we aimed to assess the efficacy of susceptibility test driven sequential therapy as the third line therapy for those who fail from two standard eradication therapies. 