Reactivation of hepatitis B virus (HBV) following immunosuppressive therapy or hematopoietic stem cell transplantation is a potentially fatal complication that may occur even in patients with prior resolution of HBV infection. Dasatinib is a small-molecule inhibitor of the tyrosine kinases SRC and ABL that has been approved for the treatment of chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia. Here, we report the first case of reactivation of resolved infection with the HBV immune escape mutant G145R in a CML patient receiving dasatinib. Although dasatinib is not recognized as an immunosuppressant, our observations suggest that dasatinib may enhance HBV replication and induce its reactivation in immunocompetent patients, that HBV escape mutants may contribute to the pathogenesis of HBV reactivation, and that close monitoring of HBV status is advisable in patients with current or resolved HBV infection.