Khammouane or Khammouan (Lao: ຄໍາມ່ວນ) is a province of Laos, located in the center of the country. Its capital lies at Thakhek.

Khammouane Province covers an area of 16,315 square kilometres (6,299 sq mi) and is mostly of forested mountainous terrain. The province is bordered by Bolikhamsai Province to the north and northwest, Vietnam to the east, Savannakhet Province to the south, and Thailand to the west. Many streams flow through the province to join the Mekong River. The vast forests of the Nakai-Nam Theun Biodiversity Conservation Area are an important watershed that feed many Mekong tributaries as well as form the catchment area for Nam Theun 2, the largest hydropower project in Laos. The Xebangfay, Hinboun and Nam Theun are the main rivers of the province.