Kaposiform hemangioendothelioma (KHE) is a rare vascular neoplasm that can be potentially low malignant and mainly affects infants and adolescents. This tumor usually is seen in the skin, soft tissue, and retroperitoneum. This study is a case of KHE in the long bone of the ulna. The subject was a 7-year-old female patient with osteolytic lesion in the forearm without cutaneous lesions. Histologically, the neoplasms comprised of nodules of spindle-to oval-shaped cells that grew in an infiltrative fashion. The results of 2-year follow-up of the patient after enblec resection were desirable and no recurrence was observed. This is the first study to report a case of KHE of the bone in Iran.