Onobrychis avanakensis is described as a new species in sect. Onobrychis. The new species is restricted to the Alborz Mountains in the Qazvin province of Iran and distinguished from its closely related taxa in both morphological and molecular evidence based on nrDNA ITS sequences. O. avanakensis is well distinct from O. major and O. carduchorum by having different sizes of keel, wing and calyx. Based on the phylogenetic tree resulted from Bayesian inference, the new species is located in a separate branch. The distribution map and an illustration of the new species are provided.