Sections of the West Highland railway line will be closed on six separate occasions so an £8m improvement programme can be carried out.
Sections of the West Highland line will be closed from 29 March
Network Rail said the work - which includes refurbishment of viaducts and laying new track - would improve the reliability of services.
Closures will take place on different dates from 29 March until 4 May.
First ScotRail said buses would be provided for passengers when train services were affected.
The first closure will be between 29 March and 13 April to allow engineers to carry out earthwork, rock stabilisation and vegetation projects at various sites between Fort William and Mallaig.
A week-long closure of the line between Crianlarich and Oban will follow between 19 and 27 April.
Major projects include strengthening and painting of the Manse, Glen Falloch and Glen Fillan viaducts.