Slieve Binnian (from Irish Sliabh Binneáin, meaning 'mountain of the little peaks')[1] is one of the Mourne Mountains in County Down, Northern Ireland, 9 km north of Kilkeel.

The summit is broad and flat with rocky tors at the north and south ends, with the Back Castles, impressive towers of granite, in between.

[2][3] To the south-west is Wee Binnian (from Irish Broinn Bhinneáin, meaning 'breast of Binneán') (460m).

[2] The mountain is in the townland of Brackenagh East Upper (379 acres), the civil parish of Kilkeel and the historic barony of Mourne.

A workforce of 150 was involved in two tunnelling teams which started from opposite ends and met in the middle nearly 800m under the roof of the mountain.