Officers from British Transport Police and ambulance services were called out to the line close to Denaby Level Crossing near Doncaster just after 8am this morning.
A BTP spokesperson said: "Officers were called to the line close to Denaby Level Crossing, near Doncaster, on Sunday, April 23, after concerns were reported for a possible body trackside.
"Officers from the BTP and South Yorkshire Police attended the incident, which was reported to BTP at 8:12am.
"Medics from the local ambulance service also attended but the person was pronounced deceased at the scene. A file will be prepared for the coroner. Enquiries are ongoing."
The incident caused disruption to train services between Sheffield and Doncaster. the line is due to be reopened early afternoon today.