A 73-year-old man contracted acute hepatitis E with decreased platelet count in the course of chemotherapy against advanced gastric cancer and administration of corticosteroid for adverse effects of chemotherapy. After the recovery of hepatitis, he underwent the first administration of Nivolumab, and subsequently died of bleeding from the cancer by immune-mediated severe thrombocytopenia. The relationship between the thrombocytopenia after Nivolumab therapy and prior hepatitis E virus (HEV) infection cannot be excluded. The patient ate pig offal before hepatitis E, and the HEV strain obtained from the patient was of genotype 3b, which was prevalent in Japanese pigs. HEV infection should be considered as the cause of liver dysfunction and thrombocytopenia during chemotherapy or treatment by immuno-suppressive agents.