This report describes a 49-year-old male patient who presented with a pituitary adenoma extending to the suprasellar region. Subarachnoid hemorrhage (SAH) occurred after conventional transnasal transsphenoidal surgery for a non-functioning pituitary adenoma despite no suprasellar arachnoid membrane breakdown. Through extended transsphenoidal route, the suprasellar hematoma was removed and bleeding from a small vessel thought to be the branch of left superior hypophyseal artery was successfully controlled. Indeed, several case reports regarding this rare complication have been published, but the mechanism of SAH has never been identified and the prognosis was poor in most cases. This report illustrates the origin and mechanism of the bleeding clearly using the intraoperative video. This case suggests that immediate therapeutic intervention is necessary and extended transnasal transsphenoidal repeat surgery is useful for an appropriate hemostasis and removal of hematoma located in the suprasellar region.