A 55-year-old female with 3 month history of blurred vision. Six days PTA, she developed epistaxis, ptosis both eyes while her eyesight deteriorated. Her consciousness was intact. Cranial nerves examination found defects of bilateral CN III/IV/VI, impaired VA. Other neurological examinations were all intact. CT scan of the brain showed the heterogenous enhancing mass at sellar-suprasellar region about 3.3.x4.9x3.2 cm, obliterated prepontine cistern and both optic chiasm. 50% of the tumor was removed using an endoscopic transnasal transphenoidal method. Pathology result was compatible with giant cell tumor of bone(GCTB). Her blood tests were normal, excepted hypercalcemia (10.6 mg/dl) hypophosphatemia with nonsuppressible PTH (67.42 pg/mL, NR 11-62 pg/mL) which mean she had primary hyperparathyroidism. Since the pathological study could not discriminate between GCTB and brown tumor. Moreover, co-existing between primary hyperparathyroidism and GCTB was rare and complete resection was not feasible. Hence, brown tumor was more likely and parathyroidectomy was the choice. Parathyroid MIBI scan found abnormal uptake spot at left lower lobe of thyroid suggestive of parathyroid hyperplasia. Focused left inferior parathyroidectomy was successful. PTH level after operation was within normal range (18.8 pg/mL). 6 weeks after surgery, she became comatose with GCS of E1V1M1. MRI scan showed progressive disease, compressed to brainstem. We started denosumab (120 mg SC). Within 3 weeks her consciousness regained, she was able to respond to verbal command and she could be discharged and continue rehabilitation. Follow-up MRI scan,1 month after treatment, showed tumor response. In June 2018, the patient clinically improved, no headache, slowly recover her visual acuity. GCTB is a rare bone primary tumor with unique characteristics. This case was life-threatening, rare primary tumor at base of skull and rare coexisting of primary hyperparathyroidism led to misdiagnose as a brown tumor. Denosumab provided remarkable response and successfully saved her life.