As part of taxonomic revision of Flemingia (Fabaceae), we describe and illustrate F. langbiangensis T.V. Do, B. Xu & X.F. Gao as a new species from southern Vietnam. Flemingia langbiangensis is morphologically similar to F. latifolia, F. ferruginea and F. macrophylla, but it differs from those by glabrescent branchlets; a subcapitate-like raceme with flowers condensed to the apex; a broadly ovate bract about half of the calyx length, 5–6 × 4–5 mm, densely brownish villous outside, with black glands inside; subsessile flowers with a greenish to pink corolla that is as long as or slightly longer than calyx; and pods that are of the same length as calyx. Additionally, F. prostrata Roxb. is lectotypified and together with F. sootepensis reported as new for Vietnam. A diagnostic key to the twelve Vietnamese species of Flemingia is provided.