Optimal perioperative management in patients with idiopathic thrombocytopenic purpura (ITP) necessitates a therapeutic approach to increase the platelet count and reduce the risk of hemorrhagic complications. We report a case of an unruptured cerebral aneurysm accompanied by ITP in a patient who received high-dose intravenous gamma globulin (IgG) therapy before clipping surgery. A 53-year-old man underwent clipping surgery for an unruptured anterior communicating artery aneurysm, which showed enlargement during follow-up. The patient was diagnosed with chronic ITP three years before presentation. However, he did not receive any medication and was only followed up. The patient had a history of anaphylactic reaction secondary to platelet transfusion; therefore, we administered high-dose IgG therapy to increase the platelet count perioperatively. High-dose intravenous IgG therapy (400 mg/kg/day) was administered for five consecutive days before clipping surgery. As a result, the patient’s platelet count increased from 1.9 × 104/mm3 at admission to 12.7 × 104/mm3 two days preoperatively. He underwent successful clipping surgery without any peri- or post-operative complications. His platelet count was maintained at >10.0 × 104/mm3 perioperatively and gradually reduced to 5.5 × 104/mm3 three weeks postoperatively. IgG therapy may be a useful treatment strategy for perioperative management in patients with ITP, particularly in cases that can be carried out semi-electively, such as in the present case.