There is a reduced service between Didcot Parkway and Reading due to overhead electric line problems at the Oxfordshire station.
Fewer trains are able to call at Cholsey, Goring And Streatley, Pangbourne and Tilehurst.
Disruption is expected to last throughout today (Monday, January 15).
A Great Western Railways spokesperson said: “Due to damage to the overhead electric wires at Didcot Parkway, fewer trains are able to run.
“Train services running through this station may be cancelled, delayed or terminated at and started back from Reading.
“Some stations between Reading and Didcot Parkway will not be served.
“Disruption is expected until the end of the day. Please check before you travel at http://gwr.com/check”