Aneurysms of the posterior cerebral artery are rare, furthermore giant serpentine aneurysms-partially thrombosed aneurysms containing a tortuous vascular channel-of the posterior cerebral artery are extremely rare. The author et al. were able to remove 3.9cm x 2.9cm x 3.0cm sized giant serpentine aneurysm of the distal PCA totally, without any significant postoperative neurological sequela except transient ipsilateral third cranial nerve paresis and transient hemihypesthesia. Various kinds of surgical treatment were proposed by several authors in managing unclippable giant aneurysms:excision including partial excision;clipping of feeding artery and excision;trapping and excision;revascularization and excision;anastomosis only. We took subtemporal approach under the surgical microscope and trapping & excision was performed in several steps:proximal clipping of the PCA distal to the Pcom-PCA junction;reducing volume of the mass through piecemeal resection of the aneurismal wall;distal clipping of the PCA;total excision and final trapping just proximal and distal to the origin of the aneurysm. We are discussing the characteristics of the giant serpentine aneurysm, precognition of rich collateral circulation of the PCA distal to trapping and surgical management of the giant serpentine aneurysm.