Abstract This research consists of the taxonomic-floristic treatment of taxa of Mimosoideae occurring in the Brazilian Chaco. The specimens analyzed were collected from 2004 to 2012 in Chaco remnants located in southwestern Mato Grosso do Sul, Brazil. Mimosoideae is represented by 39 taxa belonging to 14 genera; among the most representative, Mimosa (16 taxa) and Prosopis (4 taxa) are highlighted. Chloroleucon chacoense, Mimosa centurionis and Prosopis alba are new records for the Brazilian Flora. Prosopis nigra has its occurrence expanded. Mimosoideae is the second subfamily in species richness compared with other subfamilies of Leguminosae studied in the Brazilian Chaco. This work includes morphological descriptions, identification keys, illustrations and taxonomic comments.