Onobrychis alamutensis Amirah., Kaz. Osaloo & Charkhch. is described as a new species. It is restricted to the northwestern Alborz mountain range in Rudbar-Alamut, Qazvin, Iran. The diagnostic characters and relevant description of the species are given. The new species is distinguished from its closely related taxa, Onobrychis verae Sirj., O. ptychophylla Sirj. & Rech.f., and O. sosnowskyi Grossh. in both morphological and molecular evidence (nrDNA ITS sequences). The distribution map and an illustration of the new species are also provided.