The Pole, a former cross-country MTB world champion and a two-time Olympic silver medalist, finished runner-up in the women's race on Saturday, 1 minute 13 seconds behind Austria's Mona Mitterwallner, who completed the 80-kilometre course in 4:48.54.
Spain's Natalia Fischer Egusquiza came in third, with a time of 4:56.31.
After the race, the 37-year-old Polish rider shared a social media post in which she said she "had an amazing last race."
"Thank you and good bye! See you on the other side of the tape," she wrote.
She added: "Wonderful journey comes to the end. Hope that a lot of beautiful new adventures are coming."
Włoszczowska was this summer elected to join the Athletes' Commission of the International Olympic Committee (IOC), becoming the second Pole, after the late Irena Szewińska, to take the prestigious role at the international Olympic body.
The 37-year-old in August finished 20th in the Olympic mountain-bike event in Tokyo, and has called an end to her sporting career as she focuses on new duties.
Włoszczowska won a world championship in cross-country mountain biking in 2010.
She won the silver in the women’s mountain bike race at the 2016 Olympics in Rio de Janeiro. She also took the silver at the 2008 Beijing Olympics.
(gs)
Source: PAP