Isabeau of Brittany (in French Isabeau de Bretagne) (1478-10 June 1490^[1]), was the younger daughter of Francis II, Duke of Brittany and Margaret of Foix. She was, during her life, her sister Anne of Brittany's heir to the Duchy of Brittany.^[a]

She lived in the Château de Nantes. She was betrothed to Jean d'Albret in 1481, but he married Catherine of Navarre instead. She was eight years old when her mother died. She was 10 years old when her father died. She died in 1490 at the age of twelve years from pneumonia. She was buried in the Rennes Cathedral.