Acanthus austromontanus is a species of flowering plant in the genus of Acanthus. It is native to southwestern Tanzania and typically exists as a shrub.
It measures in height, with young, slightly hairy stems. Its elliptic leaves are up to long and have spiny edges along with an acute, spine-tipped apex. The undersides are sparsely hairy with glossy veins, while the tops are mostly smooth. Flower clusters (cymes) grow up to , with purple-tinted bracts lined with teeth.