British Transport Police (BTP) said the incident happened at the Gipsy Lane level crossing, Needham Market, near Ipswich at about 14:00 BST.
The woman was struck by the Liverpool Street to Norwich service, officers said.
Paramedics from the East of England Ambulance Service were called to the scene but the woman was pronounced dead.
A BTP spokesperson said: "Officers are currently on scene working to establish the identity of the deceased and inform her next of kin.
"The incident is currently being treated as non-suspicious and a file will be prepared for the coroner."
A woman has been killed on a level crossing in Suffolk.