Prostanthera rotundifolia (roundleaf mint bush) is a species of flowering plant in the family Lamiaceae, one of about 90 Australian endemic species from the genus Prostanthera. Its native distribution is in South Australia, New South Wales, Victoria and Tasmania. The species is listed as vulnerable in Tasmania. It is an evergreen, branched shrub, which may reach up to 4 m (13 ft) tall by 3 m (10 ft) broad. It has dark green, strongly aromatic, round leaves 4–10 millimetres (0.16–0.39 in) long, and cup-shaped purple flowers 1 cm across between September and October.