Northbound train No. 261 struck the San Mateo resident on the tracks at East Bellevue Avenue at about 4:40 p.m., according to Caltrain spokeswoman Tasha Bartholomew.
Trains were temporarily single-tracked through the area at reduced speeds following the crash, but northbound and southbound tracks were both open as of 6:30 p.m.
The cause of the crash remains under investigation, according to the coroner's office.
The crash marks the 12th Caltrain-involved fatality this year.