In double eyelid blepharoplasty, unexpected bleeding may cause intraoperative hematoma, swelling, and temporary ptosis, which could cause asymmetry and prolong recovery time. In 1725 patients (3450 eyes), double eyelid blepharoplasties were performed on Chinese patients from January 2014 to July 2016 by our senior author. In 36 eyes, the authors identified a variant artery, which the authors named the “sentinel artery,” located in the inferolateral superficial orbital septum. The sentinel artery courses between the orbital septum and the levator palpebrae finally drain into the peripheral arcade. This artery is uncommon since only 1.04% of eyes have it. If the artery is severed accidentally, the cleaved arterial end will retract into the levator palpebrae and bleed causing a large hematoma to rapidly form posterior to the levator palpebrae. The authors actively avoided unexpected bleeding caused by tearing up this artery while opening the orbital septum during double eyelid blepharoplasty procedure.