The child was found wrapped in a woollen shawl and pyjama top, placed in a plastic shopping bag, in the last carriage of a train headed to the town of Baiano from Naples, Il Mattino reported.
The baby was found by the train’s conductor and taken to Moscati hospital in Avellino, where staff have named him Carmine.
Weighing almost 2.5 kilos, doctors said the child is “healthy”, while tests showed he was breast-fed soon after being born.
“Over the course of my career on the trains I’ve found everything, from mobile phones to fish in shopping bags,” the conductor, Antonio, was quoted in Il Mattino as saying.
“Who would have thought that one day I would find a baby.”
Police are now searching CCTV on the Metrostar Circumvesuviana train to see if they can identify who abandoned the baby.
Last October, mechanics carrying out repairs on a car south-western France found a dehydrated baby girl in the car boot.