ScotRail has started rolling out it's newly-refurbished Class 334 trains on the route via Airdrie and Bathgate.
Four trains have been introduced after makeovers as part of a £4million programme.
The project will also see a further 36 refurbished trains being phased in during the next two-and-half years.
The overhaul is aimed at improving passenger comfort and includes re-covered seats, new flooring and upgraded interior finishes.
Each of the trains has been rebranded in the new 'ScotRail, Scot-land's Railway' livery.
The overall contract was awarded to Railway Projects Limited, but much of the work is being carried out by Kilmarnock sub-contractor Brodie Engineering.
Its depot in Ayrshire has undergone exten-sive refurbishment and extension to facilitate the ScotRail contract.
The work is expected to be completed by October 2014.
Steve Montgomery, ScotRail's managing director, said: "The enhancements mean that our customers can travel in greater comfort.
"It also supports Transport Scotland's ongoing roll out of a new, consistent brand for Scotland's railway."
Transport Minister Keith Brown said: "I am delighted to see that the newly refurbished trains have begun returning to service, offering passengers a more comfortable and attractive rail journey.
"The Scottish Government is comm-itted to encouraging as many people as possible on to public transport and the improved on-board environment on these Class 334 trains will go towards achieving that vision."