Square Élisa-Mercœur, Public garden near Château des Ducs de Bretagne, Nantes, France.

Square Élisa-Mercœur is a public garden in central Nantes, split into two parts by Rue de Strasbourg. It lies south of the Château des Ducs de Bretagne and east of the Île Feydeau. The western part holds a fenced children's play area with a 30-metre acacia-wood dragon by Kinya Maruyama, while a 1,300 m² water mirror faces the castle along the tram line.

The square developed after World War II on reclaimed embankments along the Loire River and was named in 1968 to honor the local poet. This naming reflected the city's recognition of her contribution to literary history.

The square is named after Nantes poet Élisa Mercœur (1809–1835). Since 2013 it has held Éric Fonteneau's bronze 'Un arbre, la forêt', showing birds of the Loire banks perched in slender tree trunks. The western part holds a fenced play area with a 30-metre acacia-wood dragon by Japanese artist Kinya Maruyama, inaugurated on 15 July 2014 and based on drawings by pupils of the nearby Émile-Péhant school.

The square is split in two by Rue de Strasbourg, which runs north from the roundabout where the two cours meet. A pedestrian underpass beneath the Nantes/Saint-Nazaire railway line, fitted with lifts at both ends, links the roundabout to Allée Baco. The western part holds the fenced children's play area.

The large water mirror installation of around 1,300 square meters facing the castle creates constantly changing reflective surfaces throughout the day. This ever-shifting effect makes each visit feel different depending on light and weather conditions.