The woman had been sledding with her husband down the winding Oberalpstrasse sledge route towards Andermatt, in the central canton of Uri, when she missed a turn and fell over a rock face, regional police said in a statement.
She had plunged onto the tracks of the Matterhorn Gotthard Bahn railway and suffered fatal injuries, the statement said.
Following the accident, the railway line was closed for around 90 minutes, it added.
Riding on a separate sled, her husband had followed the designated route, the ATS news agency reported.
The Uri police said the cause of the accident was unknown and under investigation.