Mimosa arturoana (Mimosoideae, Leguminosae) is described and illustrated for the first time. This species is similar to the recently published M. lamolina and to the allopatric, Mexican M. deamii, but differs by several morphological characters, such as stems armament, secondary venation of leaflets and pubescence of vegetative organs and pods. This species should be included in the Mimosa sect. Mimosa ser. Mimosa subser. Lactifluae by its characteristic habit, armament of stems, and ecology. This finding increments the diversity of Leguminosae in the dry forests of Inter-Andean valleys of Peru, a potentially center of endemism of this family.