Sainte-Marie-sur-Mer (Breton: Lokmaria-Pornizh) is a former commune in the Pays de Retz, situated in the Loire-Atlantique département and in the French région of Pays de la Loire. From 1973, it was absorbed by the neighbouring commune of Pornic and from 1 July 2007 it became a subdivision of this commune.
The commune forms a part of Brittany, in the traditional county of Retz and in the historical Pays Nantais.
The inhabitants of Sainte-Marie are known as the Sanmaritains and Sanmaritaines.