Three new species of Mimosa (Leguminosae, Mimosoideae), from the campos rupestres of the state of Minas Gerais, Brazil, are described and illustrated. The species are from section Batocaulon DC. (Mimosa mitzi and Mimosa rubra) and section Calothamnos Barneby (Mimosa longistipula). Mimosa longistipula is similar to M. flocculosa but mainly differs from it by the stellate trichomes found throughout its corolla. Mimosa mitzi is morphologically similar to Mimosa hexandra and Mimosa exalbescens. However, it can be distinguished from M. hexandra by its free stamens and the presence of paraphyllidia, and from M. exalbescens by the larger leaves and smaller number of leaflets. Mimosa rubra is morphologically similar to M. minarum, but is easily recognized by the reddish color of its stems and leaves. The three species described here are restricted to the state of Minas Gerais and are critically endangered according to the IUCN criteria. A discussion on the distribution, habitat, phenology, conservation status, etymology, and notes about morphologically similar species is provided, along with keys to their closest relatives.