Mayor Yannick Moreau announced the move on Facebook on Tuesday, criticizing what he described as "indecent behavior" from half-dressed visitors.
"It's a matter of respecting the residents who don't want people roaming the streets half-naked," Moreau wrote. "It's also a basic hygiene rule for our shops, markets, and public spaces."
He urged local police to ensure the measure is enforced.
For those keen to show off their swimsuits or physiques, Moreau noted that the town offers 11 kilometers of beach, CNN reported.
The post included a poster stating the fine and the slogan: "In Les Sables d’Olonne, respect doesn’t go on holiday."
Many locals voiced their support on Facebook.
"Thank you, mayor. I find this completely intolerable," wrote one user.
Another commented: "My parents are shopkeepers, sometimes they ask people to get dressed."
Les Sables d’Olonne joins other French towns taking similar steps to maintain public decorum.
Arcachon, another west coast holiday destination, has also implemented a €150 fine for public nudity or partial dress away from the beach.
In the south, La Grande-Motte has adopted the same rule for areas beyond its beach and seafront promenade.
In 2023, the Spanish city of Malaga announced fines of up to €750 ($874) for individuals found in public areas without clothes or dressed only in underwear. The city also launched a billboard campaign to remind tourists to dress appropriately.