Astragalus rattanii is a species of milkvetch known by the common name Rattan's milkvetch. It is endemic to northern California, where it grows in the North Coast Ranges.
This is a hairy annual herb with thin stems growing up to long. The leaves are a few centimeters long and made up of a few oval-shaped leaflets. The inflorescence is a head of two to ten flowers which are pinkish purple in color with paler tips. This fruit is a cylindrical legume pod up to long with a sharp, pointed beak at the end.