Ancenis is a commune in the Loire-Atlantique department, western France. It is department's sub-prefecture. In 2009, the population of Ancenis was 7,550 in a total area of 20.07 km2 (7.75 mi2).
Ancenis played a very important historical role as a key location on the road to Nantes, the historical capital of Brittany, which is 37 km (23 miles) to the southwest. It was named "the door of Brittany" and "the key of Brittany".
Sights of interest in Ancenis include the medieval and Renaissance castle Château d'Ancenis, Loire river on which Ancenis is situated (on the north bank), Chapel of the Ursulines, Church of Saint Peter, Chapel Notre-Dame de Delivrance, Dolmen at Pierre-Couvretiere, Old quarter with medieval houses.