A giant intracranial internal carotid artery(ICA)aneurysm is difficult to treat. We encountered a case with an unruptured giant intracranial ICA aneurysm with a ruptured C2 aneurysm of the ipsilateral ICA. In this case report, we describe how the treatment and review the literature. A 59-year-old man presented with sudden-onset headache and vomiting. He was diagnosed at a local neurosurgical unit as having a subarachnoid hemorrhage and admitted to our hospital. Cerebral angiogram revealed an unruptured giant ICA C3-4 aneurysm with a ruptured aneurysm of the ipsilateral ICA C2. The ruptured aneurysm had a wide neck and was located in the medial wall of the ICA C2;it was difficult to perform neck clipping or coil embolization. We performed a high-flow bypass using a radial artery graft followed by trapping of the left ICA. Postoperative imaging showed no new ischemic damage, and the patency of bypass flow was good. The left ophthalmic artery was perfused from the external carotid artery. Although the patient experienced incomplete left oculomotor nerve palsy and left lower quadrantanopsia, his neurological function had recovered within a year, and he was able to resume his previous work. High-flow bypass with ICA trapping is effective for ICA giant aneurysm. Attention to postoperative ophthalmic function and oculomotor symptoms is important.