Sedum matsuense, a new species from the Matsu Islands, is described. This species is only found in Peigan Island and Dongju Island. Previously, this species has been misidentified as S. lineare. However, they can be easily distinguished by phyllotaxy (alternate vs. 3- or 4-verticillate) and leaf shape (linear-lanceolate to oblanceolate, apex acute vs. linear, apex subacute). The phylogenetic analysis also indicates that S. matsuense is distantly related to S. lineare and to the other resembling species. In this paper, to aid in identification, we provide descriptions, photographs, and line drawings.