Aim:The authors observed the nostril lfoor in a gross cadaver specimen histologically and innovated a medially based de-epithelialized lfap for nasal base narrowing and nostril sill augmentation. Methods:In cadaver, fully thick section was taken from the nostril sill at the midpoint of the columella base and ala base, and stained with Masson-Trichrome. In eight patients, circumferential incision along the nostril sill and alar base freed the alar base from the upper lip. At the columellar base, fresh epithelium was shaved on the medial side of the incision line. The widened scar on the upper lip was excised. The de-epithelialized tip of the columellar base was pulled under the medial tip of the alar base lfap and sutured tightly. Four anthropometric distances were measured preoperatively and postoperatively. Results:Histologically the nostril sill was composed of thickened dermis. Just below the dermis, the depressor septi nasi muscle ran obliquely, augmenting the nostril sill. The nostril lfoor width, alar distance, and alar curvature distance decreased on the cleft side after the operation. Conclusion:A medially based de-epithelialized lfap narrows the alar base and augments the nostril sill simultaneously, since the de-epithelialized part of the excess skin augments the depressed nostril sill.