Castelmoron-d'Albret (French pronunciation: [kastɛlmɔʁɔ̃ dalbʁɛ]; Occitan: Castèlmauron d'Albret) is a commune in the Gironde department in Nouvelle-Aquitaine in south-western France.

It is notable for being the smallest commune in France by size, with an area of just 3.54 hectares (8.75 acres), roughly the size of the Place Charles de Gaulle in Paris.

By comparison, the largest commune in metropolitan France is Arles, with an area of 759 km2 (293 sq mi).

It is the smallest commune in France, and is smaller than the nations of Monaco and Vatican City.

This Gironde geographical article is a stub.