Saint-Marc-sur-Mer is a seaside resort in France, situated in the commune of Saint-Nazaire (principal place of the arrondissement of Saint-Nazaire, in the department of Loire-Atlantique, region of Pays de la Loire). It is located 6 kilometres (3.7 mi) to the west of the center of the town of Saint-Nazaire, of which it is a district. Originally named Crépelet, at the end of the 19th century the town was given the name of the saint to whom its chapel was dedicated.