All routes between Cardiff and Newport and Arriva Trains Wales services between west Wales and the Valleys are subject to alteration.
No trains will run between Cardiff Central and Cardiff Queen Street.
Passengers had faced cancellations and delays before new year as a result of re-signalling work in Cardiff Central.
Changes include:
Engineering works for the Christmas period are scheduled to be completed before 3 January.
Rail passengers in south Wales are being advised to check before they travel as a number of services have temporary changes to their timetables.