Network Rail said engineering works over the festive period will affect some routes in Sussex.
This will include a major upgrade that will close London Victoria to Southern and Gatwick Express services and alter services on the railway west of Brighton.
A major signalling upgrade will take place on the west coastway line between Brighton and Littlehampton during the weekend before Christmas.
The work means trains will be replaced by buses on Saturday, December 22 and Sunday December 23.
Network Rail is using the planned closure to install a new footbridge at Fishersgate station, replacing the old structure which will be removed at the same time.
The new bridge will be transported to site by rail from Hove station in sections before being craned into place.
And Platforms 9 to 19 will be closed at London Victoria station from 1.05am on Sunday, December 23 until 4am on Wednesday, January 2, with no trains between the station and Clapham Junction.
Most Southern trains will be rerouted to and from London Bridge.
John Halsall, Network Rail’s South East route managing director, said: “This Christmas we’re continuing with major parts of our Railway Upgrade Plan in the south east, aimed at providing a better, more reliable railway to the growing number of people who travel by rail.
“The work we’re doing at Battersea and on the coastal route in West Sussex are critical pieces of the jigsaw to help us provide the infrastructure passengers deserve, reducing delays and boosting reliability.
“Of course, we know it’s never a good time to close the railway but doing nothing is not an option either. Doing the work over the Christmas holidays, when the railway is significantly quieter than usual, means we can minimise overall disruption to passengers.”
Angie Doll, Southern and Gatwick Express passenger services director, said: “Passengers need to be aware of this essential work which closes London Victoria to our services from Sunday, 23 December, all the way through to Wednesday, 2 January.
“We will be working very hard to keep passengers moving to and from Gatwick Airport and the capital with many services diverted into London Bridge and London Blackfriars but there will be no Gatwick Express service and fewer Southern trains than normal.
“Passengers should check before they travel.”
To find out more, visit: nationalrail.co.uk/christmas