Batz-sur-Mer (French pronunciation: [ba syʁ mɛʁ], literally Batz on Sea; Gallo: Borg-de-Baz, Breton: Bourc'h-Baz) is a commune in the Loire-Atlantique department in western France.

The territory of the commune is now part of the wild coast of the Guérande Peninsula with rocky cliffs, sandy beaches along the Atlantic Ocean and extensive salt marshes to the northeast and east.

Its Benedictine monks developed the local economy and apart from religion they devoted themselves to agriculture and to the maintenance of salt ponds.

[6] Batz was historically part of the Duchy of Brittany and is very near the south-eastern limit of the area in which there is evidence of Breton settlement in the early Middle Ages.

He wrote there Un drame au bord de la mer,[8] which is set in nearby Le Croisic.