Saint-Martin-en-Campagne is a former commune in the Seine-Maritime department in the Normandy region in northern France. On 1 January 2016, it was merged into the new commune of Petit-Caux.

A coastal farming village situated in the Pays de Caux, at the junction of the D113, D313 and the D925 roads, some 5 miles (8.0 km) east of Dieppe. Huge chalk cliffs rise up over a pebble beach and overlook the English Channel. The Penly Nuclear Power Plant is also sited in this commune.

The arms of Saint-Martin-en-Campagne are blazoned : Gules, a sword, on a chapé argent a lion and an alerion gules, and on a chief azure, a seagull proper.

Historical population

Year	Pop.	±% p.a.
1962	484	—
1968	544	+1.97%
1975	562	+0.47%
1982	833	+5.78%
1990	1,104	+3.58%
1999	1,000	−1.09%
Source: EHESS

• The church of Notre-Dame, dating from the fifteenth century.
• A stone cross from the sixteenth century.
• The Penly Nuclear Power Plant on the coast, with two reactors of 1300 MW each.

• Communes of the Seine-Maritime department