Cayeux-sur-Mer (French pronunciation: [kajø syʁ mɛʁ], literally Cayeux on Sea; Picard: Tchéyeu-su-Mér) is a resort town in the Somme department in Hauts-de-France in northern France.

The town is part of the Baie de Somme - Picardie maritime regional natural park project.

The town of Cayeux-sur-Mer is located on the Picardy coast, in the natural region of Marquenterre, south of the Baie de Somme, 16 miles west of Abbeville as the crow flies.

The boardwalk, lined with around 400 colorful cabins and 2 km long, offers a pleasant setting for walking and relaxation.

The town is at the end of the tourist line of the Somme Bay Railway linking Le Crotoy - Noyelles-sur-Mer - Saint-Valery-sur-Somme and Cayeux-sur-Mer.

The town hall of Cayeux-sur-Mer is a brick building with openings framed in white stone.