Montarnaud () is a commune in the Hérault department in the Occitanie region in southern France.
Montarnaud has a mediterranean climate (Köppen climate classification Csa). The average annual temperature in Montarnaud is . The average annual rainfall is with October as the wettest month. The temperatures are highest on average in July, at around , and lowest in January, at around . The highest temperature ever recorded in Montarnaud was on 28 June 2019; the coldest temperature ever recorded was on 16 January 1985.