Approximately 20-30% of cancers are associated with hypercalcemia, and this is a complication often encountered in cancer care. Hypercalcemia causes disorders such as disturbance of consciousness and, in severe cases, kidney failure and even death. In this report, we present a case of malignant ameloblastoma associated with uncontrollable hypercalcemia followed by a life-threatening disease course. In this case, hypercalcemia shortened the period of home care, and the medical staff could have extended this period by acquiring knowledge that leads to early detection and better control of hypercalcemia. In addition, the choice of the place for end-of-life care may have been expanded by considering the treatment of not only the malignant tumor but also hypercalcemia as its complication.