The work will affect trains from January 6 through to January 10.
We have compiled all the details on these works so that you can plan your journey this week.
Monday to Friday (January 6 to January 10):
Engineering work is taking place overnight between Brighton, Worthing and Littlehampton ending Friday morning, closing all lines.
From 11.45pm until the end of service on Monday to Thursday evenings, replacement buses will run between Brighton and Worthing / Littlehampton.
Trains from London Victoria to Littlehampton will be diverted to Brighton, for connecting replacement buses.
The 10.20pm train from Southampton Central to Brighton will not call at Southwick or Portslade.
Passengers should change at Shoreham for a replacement bus to Brighton, calling at Southwick and Portslade.
Journey times will be increased when using replacement buses.
Engineering work is also taking place overnight between Hastings and Ashford International ending Friday morning, closing some lines.
From 10.30pm until the end of service on Monday to Thursday evenings, replacement buses will run between Hastings and Ore, Rye and Ashford International.
Journey times will be increased when using replacement buses.
