Iran, especially the northwestern part of the country, is the center of diversity of the genus Astragalus section Hymenostegis in the Old World. A new species A. blattneri Bagheri & Maassoumi of that section from East Azarbayjan Province in NW Iran is here described and illustrated based on morphology and nuclear ribosomal DNA internal transcribed spacer (ITS) and plastid ycf1 sequence data. It morphologically resembles A. chrysostachys and A. recognitus but differs from these species by DNA sequences and several morphological characters.