Giant serpentine aneurysm(GSA) is a giant aneurysm containing a serpentine channel which enters and exits at separate sites and is continuous with the parent vessel. This 33-year-old man with a two-year history of frontal headache presented with bitemporal hemianopsia three months before admission. Suprasellar mass of computed tomography revealed a giant(3X2.5X2cm) mixed density, mimicking a brain tumor. Cerebral magnetic resonance images showed a flow void within the mass, and this was consistent with the serpentine vascular channel demonstrated by angiography. The aneurysm was revealed by surgery involving the frontobasal interhemispheric approach, left A1 & A2 were clipped and the mass of the aneurysm was removed in toto an aneurysmorrhaphy was constructed, and to preserve the distal blood flow to the left A2, the patient made an unevenful recovery.