Prostanthera stenophylla is a shrub species that is endemic to Wollemi National Park in New South Wales, Australia. It grows to between 1.5 and 2 metres (4.9 and 6.6 ft) high and has leaves that are 7 to 12 millimetres (0.28 to 0.47 in) long and 1.5 to 2 millimetres (0.059 to 0.079 in) wide. Dull green above and paler green below, leaves are covered with a dense mat of hairs and give off a strong aroma when crushed. The leaf edges are recurved or revolute. Mauve or violet flowers appear in the leaf axils in spring, with about 4 to 6 flower-bearing branchlets arising on a leafy branch to form a raceme. Individual flowers are about 8 to 12 millimetres (0.31 to 0.47 in) long.