Here we describe the use of a novel lip-to-nose flap technique for nasal planum reconstruction after tumour removal in a dog. A mast cell tumour involving the nasal planum was first resected by removing the roof and the wing of the left nasal vestibule. An interpolation subdermal plexus flap was derived from the left caudal lip with vascular contribution from the lateral nasal artery. This lip-to-nose flap was rotated into the defect via a bridging incision. The mucocutaneous junction of the lip was used to emulate the keratinised nasal planum and the buccal mucosa was sutured to be congruent with the mucosa of the vestibule. This resulted in the lip-to-nose flap successfully closing the surgical defect and giving an aesthetic appearance similar to the original nasal planum.