A 27-year-old woman with acute lymphocytic leukemia, who underwent allogeneic hematopoietic stem cell transplantation, complained of nausea and blurred vision 288 days after the transplantation. Intracranial tumors were identified on brain MRI. She received whole brain radiation after open biopsy, but she died. The tumors had characteristics of diffuse large B cell lymphoma, and she was finally diagnosed with primary central nervous system post-transplant lymphoproliferative disorder. This disease is rare and has a poor outcome. Therefore, accumulation of cases and establishment of treatments for this condition are urgently needed.