Mimosa is a very large genus with more than 540 species, which are distributed mainly in the Neotropics and are especially diverse in the Cerrado, where the genus shows high rates of endemism. The Serra do Cabral mountain range, which is part of the Espinhaço mountain range, contains representative remnants of the Cerrado and is a very important area for the genus, where at least 20 taxa of Mimosa are reported. Unfortunately, it is a threatened and over-exploited region. Here we describe a new narrow endemic species from the Serra do Cabral, Mimosa osmarii, that shows affinities with M. paucifolia var. scoparia, a sympatric taxon. The conservation status of M. osmarii was assessed as vulnerable.