This research provides a description and illustrations for a new species from the Phong Nha-Ke Bang National Park, Cynanchum quangbinhense. The distribution, habitat, phenology and conservation assessment for the species are also presented. The new species differs from closely related species, C. ovalifolium in many characters such as leaf shape, inflorescence type, fewer and smaller flowers, colour of petals, margins of the corona, and anthers appendages shape, and differs from C. kwangsiense in having small leaves, umbellate inflorescences, triangular sepals, retuse apex of petals, and plicate margin of corona. Our discovery raises the known species of this genus in Vietnam to seven. In addition, a key to species of Cynanchum in Vietnam, and notes on morphological variation of C. officinale are presented in this paper.