Inotuzumab ozogamicin (INO) showed improved treatment outcomes for relapsed or refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL) but can induce hepatotoxic adverse events. Hepatic venoocclusive disease/sinusoidal obstruction syndrome (VOD/SOS) frequently develops after allogeneic hematopoietic cell transplantation (allo-HCT), and INO is a strong pretransplant risk factor. However, VOD/SOS can occur just after INO therapy. Here, we describe a BCP-ALL patient treated with INO for isolated extramedullary relapse after allo-HCT. The patient experienced elevated liver enzymes with ascites at 21 days from the last INO dose. Although she met the criteria for VOD/SOS, the diagnosis was challenging because of her ongoing hepatic graft-versus-host disease (GVHD) and normal portal vein flow on Doppler sonogram. The radiologist suggested liver cirrhosis based on computed tomography, with VOD/SOS, liver cirrhosis, and GVHD assumed to be differential diagnoses. She received supportive care with GVHD management; however, due to progressive hepatic failure, we conducted emergent deceased-donor liver transplantation, and the pathologic findings indicated VOD/SOS. Her leukemia was stable, but she died of sepsis after 3 months. INO use is a high-risk factor for VOD/SOS, but an accurate diagnosis can be challenging due to various hepatic complications. Early diagnosis and proper management for VOD/SOS is important for improved outcomes.