Prostanthera serpyllifolia, commonly known as small-leaved mint-bush,[2] is a species of flowering plant in the family Lamiaceae and is endemic to southern Australia.

Prostanthera serpyllifolia is a prostrate to erect shrub that typically grows to a height of less than 0.5 m (1 ft 8 in) with hairy white branches.

[2][3][4][5][6] Small-leaved mint-bush was first formally described in 1810 by botanist Robert Brown, who gave it the name Cryphia serpyllifolia, and published the description in Prodromus Florae Novae Hollandiae et Insulae Van Diemen,[7][8] based on plant material collected from the southern Eyre Peninsula in South Australia.

[9][10] In 1984, Barry Conn described two subspecies of P. serpyllifolia in the Journal of the Adelaide Botanic Gardens and the names are accepted by the Australian Plant Census: Prostanthera serpyllifolia occurs in New South Wales, Victoria, South Australia and Western Australia where it often grows in mallee communities, often on limestone or calcrete.

Subspecies serpyllifolia occurs on the Yorke and Eyre Peninsulas and there is a single record from the southwest of Western Australia.