Newhaven Swing Bridge, which carries the A259 over the River Ouse, will close over five nights in August to allow testing of new electrical systems and lifting jacks.
The work is part of a scheme to completely refurbish the electrical and mechanical components of the structure, which was built in 1974.
The bridge will close to road traffic from 10pm on Wednesday 12, Thursday 13, Friday 14, Monday 17 and Tuesday 18 August 2015, reopening at 6am on the following morning on each of these dates.
A diversion route will be in place routing traffic to Lewes and the A27, via the A26 New Road and C7 Lewes Road.
There may be periods during the closure when pedestrians can cross the bridge but times will vary and cannot be guaranteed.
Cllr Carl Maynard, East Sussex County Council lead member for transport and environment, said: “It’s vital for both road traffic and shipping that the bridge operates smoothly, but its components are coming to the end of their natural life and need replacing.
“Closing the bridge overnight will minimise the impact on motorists and while there will be some temporary disruption, I’d ask people to bear with us while this essential work is completed.”
The swing bridge opens around 20 times a month at high tide, when its deck swings open 90 degrees for about 20 minutes to allow shipping to pass.
The structure is also being closed to marine traffic from Monday, August 3 to Friday, August 21 while a key phase of the refurbishment is carried out.
The scheme is expected to be completed by the end of September.