Val d'Oust (, literally Vale of Oust; ) is a commune in the Morbihan department of western France, named after the river Oust. Le Roc-Saint-André is the municipal seat. The municipality was established on 1 January 2016 and consists of the former communes of Le Roc-Saint-André, Quily and La Chapelle-Caro.
Population data refer to the area corresponding with the commune as of January 2025.