He was taken to Karolinska University Hospital in Solna with serious injuries but his life could not be saved, said police.
The man was practising paragliding on Friday evening in order to obtain a qualification. A witness said that something appeared to go suddenly wrong when the 24-year-old man was up in the air.
He descended with a curving motion and hit a tree in a wooded area, according to police spokesman David Hertz at Södertälje police.
The police are treating the incident as an accident.