The state railway firm VR is adding services to routes that have often been sold out recently, with more capacity added on the Oulu to Helsinki route.
The changes, which came into force on Sunday, will improve services between Helsinki, Tampere, Vaasa and Oulu.
There will also be additional commuter trains in the Pirkanmaa and Kymenlaakso regions, with considerable increases in frequency of trains between Nokia and Tampere.
On the flipside, westward services from Kuopio will be less frequent.
Compared to a decade ago, passenger numbers in Finland have remained pretty much constant. Last year there were a total of 13 million journeys, which compares to 13.3 million in 2008, but there has been growth in travel between urban centres.
"The big shift has been in where passengers are going," said Juho Hannukainen, VR’s planning director. "Nowadays people are travelling more between the bigger cities. The busier sections of the network are more congested and the quieter sections are unfortunately a little quieter than before."
VR says it is planning to use existing rolling stock more efficiently, and add coaches to some trains to expand capacity between Helsinki and Tampere, and cities to the north.