Plants that have been treated as Sorbus commixta on Ulleung Island, Korea, show morphological variability and their taxonomy is unclear. We extensively studied the morphology of wild populations of these plants and found that they can be distinguished from S. commixta by their larger fruits and flowers and wider inflorescences. Here we describe and illustrate them and propose them as representing a new species, S. ulleungensis. An updated key to the five Korean species of Sorbus including the new species is provided.