Questembert (French pronunciation: [kɛstɑ̃bɛʁ]; Breton: Kistreberzh) is a commune in the Morbihan department in Brittany in north-western France.

It is located approximately 25 km (16 mi) from Vannes.

Inhabitants of Questembert are called Questembertois. Its population was 7,723 as of 2018.

In 2008, 3.61% of local children attended bilingual schools in primary education, learning partly in Breton.