The Old Jarrah tree is an exceptionally large and old Eucalyptus marginata (Jarrah) tree near inside the carpark the entrance at the corner Third Road and Church Avenue in Armadale, Western Australia. It is estimated to be between 400 and 800 years old. Trees of such a great size and age are rare in and around the Perth metropolitan area, because of extensive logging of the area in the 19th century.
The tree is in fairly poor condition: about three quarters of its canopy is dead or gone, and it is less than half its normal height due to lopping. It was ringbarked by vandals in 1997, and it has responded by producing numerous epicormic shoots on its north side. Despite these issues, the tree is considered to be in a stable condition.