Rail operator South West Trains has cut services for four days in response to the latest strike action by staff.
It will not run any services between Brighton and Chichester from noon Monday to noon Tuesday and from noon Wednesday to noon Thursday.
Customers should use South Central services along the route instead of South West's 11 daily trains.
The strike action organised by the Rail Maritime and Transport Union is the latest in a series of walk-outs in a long-running dispute about pay and disciplinary procedures.
Company managers have been helping to run some trains and bus services have been provided along other routes.
A spokeswoman said: "Since another operator provides a service on the Brighton to Chichester line we are concentrating our resources in areas where there is no alternative.
"As before, South Central will be accepting our tickets so people in Sussex are advised to travel with them instead on those days affected by strike action."
Sam Dixon, Brighton station manager, said the disruption had been minimal in Sussex because South Central ran two trains every hour between Brighton and Chichester.
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