Tourists gathered in front of the Flame of Liberty monument, dedicated to Diana, and left behind flowers, photos and messages.
There was no word on how her children, Princes William and Harry are marking the anniversary.
Next month, William and wife Catherine will travel to Singapore where an orchid will be named after his mother.
Princess Diana and her partner Dodi Al Fayed died when the Mercedes they were in plowed into a pillar in the Alma Tunnel on Aug. 31, 1997. French police said driver Henri Paul, who also died, had been drinking heavily and was speeding.
The Associated Press contributed to this report.