Plouisy (; ) is a commune in the Côtes-d'Armor department of Brittany in north-western France. Plouisy is 407 kilometres from Paris.
Plouisy has an oceanic climate (Köppen climate classification Cfb). The average annual temperature in Plouisy is . The average annual rainfall is with December as the wettest month. The temperatures are highest on average in August, at around , and lowest in January, at around . The highest temperature ever recorded in Plouisy was on 9 August 2003; the coldest temperature ever recorded was on 17 January 1985.
Inhabitants of Plouisy are called plouisyens in French.