Chain Bridge, on West End Road, will be given a new lease of life thanks to works by Lincolnshire County Council.
Work will commence on Monday, July 7, to restore the existing structure over Old Hammond Beck.
The refurbished bridge will have new parapets (protective walling), waterproofing, surfacing, and extensive concrete repairs.
The project is expected to take about six weeks, and will be completed by Friday, September 1.
To allow work to be carried out safely, the road will be closed for the duration of the project.
Traffic will be diverted via the A52 Swinsehead Road, B1192 Holmes Lane, B1391 Ralphs Lane, B1397 London Road and West End Road, and vice versa.
Access will be maintained for pedestrians and cyclists.
The junction of West End Road with Chain Bridge Road and Old Hammond Beck Bank Road will remain open, but will be controlled by three-way temporary traffic measures.
Vehicles will be unable to access B&Q, Tesco, Downtown and Alban retail park from the east of the A52 roundabout, so customers must use alternative routes.
Andrew Antcliff, senior bridge engineer at Lincolnshire County Council, said: “Chain Bridge has suffered a lot of wear and tear over the years, so it’s essential we get these repairs done.
“By doing that, we can avoid the need for a brand new bridge, which would be a far more expensive and disruptive project.
“We’ve scheduled the works for the school holidays to minimise the inconvenience to motorists, and our contractor will be working extended hours at evenings and weekends to complete the improvements before the schools go back.
“At times, work will be taking place underneath the structure, so the team might not be visible. Due to the nature of the repairs, the bridge cannot be re-opened to traffic while the works are being completed to the underside.
“We apologise for any inconvenience caused, and advise people to leave additional time for their journeys.”
For the latest details on roadworks taking place across Lincolnshire, visit: www.lincolnshire.gov.uk/roadworks