The exact number of HBV/HCV co-infected patients is unknown. In many cases of HBV/HCV co-infection, HCV inhibits replication of HBV. After treatment and eradication of the dominant virus, the other one may then become active. The overall dominant effect appears to be hepatitis C over hepatitis B. Therefore, when planning treatment for eradication of HCV, the risk of HBV reactivation should be taken into account. In interferon-based therapies of patients with HBV/HCV co-infection, some cases of HBV reactivation without hepatitis were observed because IFN is effective against both viruses. In contrast, DAA treatment of hepatitis C in HBV/HCV co-infection is not well established. Currently, no clinical trials have been published regarding treatment of HBV/HCV co-infected patients with HCV DAA therapy. There is several research on HCV DAA therapy in HBV/HCV co-infection, which describes cases of HBV reactivation during and after DDA therapy for HCV. Result of the first available studies demonstrated that patients with HBV/HCV co-infection treated with DAA against HCV should be monitored for HBV reactivation during and after DAA treatment, even though HBV may be inactive at the time of treatment initiation.