La Gacilly is a commune in the Morbihan department of Brittany in north-western France. It is located on the right bank of the Aff River, about 15 km north of Redon, on the line between Vannes and Rennes, about 60 km from both. It extended on 1 January 2017 by merging with former communes of La Chapelle-Gaceline and Glénac.
La Gacilly is best known as the location of worldwide cosmetics company Yves Rocher. It was established in 1959 by a local, Yves Rocher, who also served as the mayor of La Gacilly from 1962 to 2008, when his son Jacques Rocher obtained the office.
The Yves Rocher La Gacilly Botanical Garden is located in the commune.