For the first time the railway will be open to the paying public.
It runs along a 328 yard track from a marble station inside the Vatican walls to a huge steel gate before it passes from the tiny city to join Italy's main railway link.
The railway was first opened in 1933 and used by Pope's for visits to Italy.
The Vatican did not begin using trains until the 1920's after Pope Gregory XVI described the train as a hellish invention in the 19th Century.
The station will now be open on Saturday's for weekly outings in a move by the pontiff to let the public see more of the world of the Holy See.
The hour-long trip will take pilgrims and tourists inside the Vatican to the papal summer residence just outside of Rome, Castel Gandolfo.
In 2013 Pope Francis said he would not be taking holidays there, saying he would rather work instead.
People will be allowed in the building for the first time in 400 years to see papal portraits, thrones and slippers.
Director of the Vatican's museums, Antonio Paolucci said: "Pope Francis has said he wants his people to enjoy something that has been only for him until now - it's a sign of the times."
A modern train will take over once it opens fully, to ensure there are not as many technical problems.
A return ticket is expected to cost around €40.
Local businesses are happy after the Pope chose not to use the residence two years ago and the usual influx of tourists no longer came to the area.
"We were not pleased he was not coming and I wrote to the Pope twice," said the mayor Milvia Monachesi.
Francis already let people into the residence's gardens showing off olive-groves and a Roman amphitheatre.
10,000 people visited the gardens last year, "When people are here, it is like the Pope himself is here," said Osvaldo Gianoli the garden and palace manager.
