BACKGROUND Little is known about the risk of hepatitis B virus (HBV) reactivation in patients receiving interferon (IFN)-free direct-acting antiviral agents (DAAs) for hepatitis C virus (HCV). METHODS Patients who were seropositive for HBV core antibody and who received IFN-free DAAs for HCV were enrolled. Hepatitis B virus reactivation was defined as reappearance of serum HBV deoxyribonucleic acid (DNA) ≥100 IU/mL in patients with baseline undetectable viral load, or ≥2 log10 IU/mL increase of HBV DNA in patients with baseline detectable viral load. Hepatitis B virus-related alanine aminotransferase (ALT) flare was defined as ALT ≥5 times upper limit of normal or ≥2 times of the baseline level. Hepatitis B virus-related hepatic decompensation was defined as presence of jaundice, coagulopathy, hepatic encephalopathy, or ascites. RESULTS Compared with no HBV reactivation in 81 HBV surface antigen (HBsAg)-negative patients, 2 of 12 HBsAg-positive patients had HBV reactivation (0% [confidence interval {95% CI}, 0%-4.5%] vs 16.7% [95% CI, 4.7%-44.8%], P = .015). No patients had ALT flare or hepatic decompensation. Baseline HBsAg level at a cutoff value of 500 IU/mL was associated with HBV reactivation in HBsAg-positive patients. There was no HBsAg seroreversion in HBsAg-negative patients. CONCLUSIONS Hepatitis B virus reactivation is limited to HBsAg-positive patients receiving IFN-free DAAs for HCV. Higher baseline HBsAg levels are associated with HBV reactivation. The risk of ALT flares or hepatic decompensation is low in these patients.