OBJECTIVES: Risk of Hepatitis B virus (HBV) reactivation have been increased because of advances in immunosuppressive therapies. People having previously resolved HBV infection and/or those with serum HBs-antigen positivity are likely to develop liver injuries after receiving immunosuppressive therapies. However, the risk for rheumatoid patients is still unclear. This study aims to clarify the significance of HBV reactivation undergoing immunosuppressive treatments with administrative database in Japan. METHODS: Between 1 April 2011 and 31 March 2015, adult patients had been diagnosed rheumatoid diseases (ICD-10 codes: M059$, M060$, M068$, M069$, and M35$) were extracted from the Medical Information Analysis (MIA) databank managed by the Clinical Research Center at the National Organization Hospitals (NHO) Headquarter. There are 143 hospitals nationwide run by the NHO, including both general acute-care and specialized long-term-care hospitals. All NHO hospitals provide administrative claims data to MIA periodically. Since an update of management guideline to recommend screening and monitoring of HBV reactivation for rheumatoid patients undergoing immunosuppressive therapies, we divided our research periods into two (A: September 2011 to August 2012; B: April 2013 to March 2014); then analyzed the data descriptively. The incidence of HBV reactivation was defined as a first prescription of entecavir. RESULTS:  During research periods, total of 5,823 patients diagnosed rheumatoid disease were identified. Among them, 1,255 patients in period A and 1,203 patients in period B were initiated their first immunosuppressive therapies. Entecavir was administered in 15 patients (0.2% in period A, 1.1% in period B, respectively). CONCLUSIONS: We identified possible rheumatoid patients with HBV reactivation undergoing immunosuppressive treatments from our administrative database. Because information of changes their serum HBV-DNA levels after immunosuppressive therapies is unavailable in database, we will review patients’ history and prognosis of immunosuppressive therapies in medical charts to identify the real reactivation cases.