In many extragastric manifestations with Helicobacter pylori (HP) infection, the most convincing evidences were observed in idiopathic thrombocytopenic purpura (ITP). The prevalence of HP infection in ITP was not different to general population. The high association of HP infection in ITP was reported in Italy and Japan but low in USA and UK. After eradication therapy, platelet counts response was found in over 50% of ITP cases in Japan and Italy, and about 40% in other countries. The platelet counts response following eradication was maintain for long time with drug free and the relapse case was rare. The platelet elevation reaction by eradication was not influenced by previous treatment, sex and age, but the disease duration as ITP and the platelet count before eradication were controversial factors. The main side effects of eradication were diarrhea, vomiting and skin rash. Based on these evidences, ITP guideline in Japan (2012) recommended that eradication therapy was the first choice treatment for HP positive ITP cases.