NO trains will run between Dorchester South and Poole for the next two days due to major signalling work.
Replacement bus services will run between Poole and Weymouth, supplemented by a shuttle train service between Dorchester South and Weymouth.
While the lines between Bournemouth and Dorchester South will be closed all day Saturday, May 17 and Sunday, May 18.
The normal train service will run between London Waterloo and Bournemouth.
Engineers need four days access to the lines to complete the work, according to a spokesman for South West Trains.
Passengers have been told bus services will run between Bournemouth and Weymouth this weekend.
A shuttle train service will also run between Dorchester South and Weymouth.
They have also been warned that the car park at Bournemouth station is expected to be very busy.
South West Trains said the work is an essential part of the investment programme to bring the area under modern and more reliable signalling control.
Details of timetables are available at southwesttrains.co.uk