Slieve Commedagh (from Irish Sliabh Coimhéadach, meaning 'the guarding/watching mountain') is a mountain with a height of 767 m (2,516 ft) in County Down, Northern Ireland. It is the second-highest of the Mourne Mountains, after Slieve Donard, and the second-highest mountain in Northern Ireland.

Slieve Commedagh lies to the northwest of Slieve Donard, and the two are linked by a col. The Mourne Wall passes east–west over the mountaintop, and there is a small one-room tower at the summit. There is also the remains of an ancient burial cairn on the summit. On its southern side is a group of granite tors known as 'the Castles'.

The Slieve Commedagh massif also includes the summits of Slievecorragh (to the east), Shan Slieve, Slievenamaddy and Slievenabrock (to the north).

• 
  Slieve Commedagh and the Mourne Wall viewed from the top of Slieve Donard
• 
  Slieve Commedagh (middle background) from the south
• 
  Slieve Commedagh (right) viewed from Murlough Beach

• List of mountains in Ireland