We report a case of HBV reactivation following belatacept treatment in a patient who underwent kidney transplantation in 2015 for HIV-associated nephropathy (HIVAN). Human immunodeficiency virus viral load was undetectable prior to transplantation, and CD4+ lymphocyte count was greater than 300/mL. Baseline HBV serology at transplantation was HBsAg negative, anti-HBcAb positive, anti-HBsAb 312 UI/L, and HBeAg negative/anti-HBeAb positive. Liver function tests were normal, and viral DNA was undetectable. Two years later, the patient presented with severe acute hepatitis after a progressive disappearance of anti-HbsAb, quickly followed by HBV reactivation. Immunosuppressive treatment was drastically reduced, and treatment with entecavir was started. The outcome was favorable, and HBV DNA became undetectable after 9 weeks of treatment. This is the first report of acute hepatitis related to HBV reactivation in a kidney transplant recipient treated with belatacept. The risk for HBV reactivation in patients treated with belatacept should not be underestimated, especially in those with resolved HBV infection.