Onobrychis kuchanensis Ranjbar, Hajmoradi & Karamian, a singular new species endemic to Iran, is described and illustrated. The new species belongs to Onobrychis Miller subgen. Sisyrosema (Bunge) Grossheim sect. Hymenobrychis DC. Onobrychis kuchanensis is distributed in Khorasan Province in northeastern Iran. It is closely related to O. amoena Popov & Vvedensky and is distinguished by its corolla neither distinctly striate nor purple maculate and its calyx shorter than 5 mm. The conservation status is evaluated as Vulnerable (VU) according to IUCN Red List criteria. Moreover, O. amoena subsp. meshhedensis Širjaev & Rechinger is raised to specific rank as O. meshhedensis (Širjaev & Rechinger) Ranjbar on the basis of morphological evidence. Relationships between both species and their closest relatives are discussed.