Elections to Castlereagh Borough Council were held on 5 May 2011 on the same day as the other Northern Irish local government elections.

The election used four district electoral areas to elect a total of 23 councillors.

Note: "Votes" are the first preference votes.

2005: 4 x DUP, 1 x Alliance, 1 x UUP 2011: 3 x DUP, 2 x Alliance, 1 x UUP 2005-2011 Change: Alliance gain from DUP 2005: 5 x DUP, 1 x Alliance, 1 x UUP 2011: 4 x DUP, 2 x Alliance, 1 x Green 2005-2011 Change: Alliance and Green gain from DUP and UUP 2005: 2 x DUP, 1 x SDLP, 1 x Alliance, 1 x UUP 2011: 2 x DUP, 1 x SDLP, 1 x Alliance, 1 x UUP 2005-2011 Change: No change 2005: 2 x DUP, 1 x Alliance, 1 x SDLP, 1 x UUP 2011: 2 x DUP, 1 x Alliance, 1 x SDLP, 1 x UUP 2005-2011 Change: No change