The Château de Blain or Château de la Groulais, is a mediaeval castle constructed in the 13th century and heavily remodelled in the 16th, located in the commune of Blain in the Loire-Atlantique département of France. It formed part of the frontier defences of Brittany along with the towns and castles of Vitré, Fougères, Châteaubriant, Ancenis and Clisson.