Lanleff (; ) is a commune in the Côtes-d'Armor department of Brittany in northwestern France.
Lanleff has an oceanic climate (Köppen climate classification Cfb). The average annual temperature in Lanleff is . The average annual rainfall is with December 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 Lanleff was on 19 July 2016; the coldest temperature ever recorded was on 11 December 1991.
Inhabitants of Lanleff are called lanleffois in French.