Buddleja bordignonii is a new species from southern Brazil. This species belongs to Buddleja sect. Buddleja ser. Thyrsoides, and is morphologically similar to B. cuneata, from which it can be distinguished by its leaves with attenuate base, leaf shape and length/width ratio, its longer peduncle of cymes, and pedicellate flowers. The species is restricted to one location in the Midwest region of Rio Grande do Sul, occurring in rocky shrublands in the municipality of Jari. We present here a morphological description, illustration and photographs of the new species. Also. we propose the inclusion of B. bordignonii in the IUCN Red List of Threatened Species in the critically endangered (CR) category since its habitat has been drastically reduced by human activity.