Mountain ash
Mountain ash may refer to:
- Eucalyptus regnans, the tallest of all flowering plants, native to Australia
 - Mountain-ashes or rowans, varieties of trees and shrubs in the genus Sorbus
 - Fraxinus ornus, a true ash (genus Fraxinus) also, but less commonly, known as mountain ash
 
See also
- Mountain Ash, Rhondda Cynon Taf, a town in Wales
 - Mountain Ash, Kentucky, a town in the United States