Elections to Castlereagh Borough Council were held on 5 May 2005 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.

2001: 3 x DUP, 1 x Alliance, 1 x UUP, 1 x PUP 2005: 4 x DUP, 1 x Alliance, 1 x UUP 2001-2005 Change: DUP gain from PUP 2001: 4 x DUP, 1 x UUP, 1 x Alliance, 1 x Independent 2005: 5 x DUP, 1 x UUP, 1 x Alliance 2001-2005 Change: DUP gain from Independent 2001: 2 x UUP, 1 x DUP, 1 x SDLP, 1 x Alliance 2005: 2 x DUP, 1 x UUP, 1 x SDLP, 1 x Alliance 2001-2005 Change: DUP gain from UUP 2001: 2 x DUP, 1 x Alliance, 1 x SDLP, 1 x UUP 2005: 2 x DUP, 1 x Alliance, 1 x SDLP, 1 x UUP 2001-2005 Change: No change