Khammouane or Khammouan is a province of Laos, located in the center of the country. To the north it is bounded by Bolikhamxai; to the south, by Savannakhet. To the west is the Mekong and Nakhon Phanom Province, Thailand; to the east, the Annamite Mountain Range separates Khammouan from Vietnam.

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.

Plans to build a bridge over the Mekong, connecting Thakhek to Nakhon Phanom, are progressing. Construction is set to begin in 2008 and will take three years to complete.

In 1996 western scientists collected an undescribed rodent representing a mammal family that had been previously known only from fossils. The Laotian Rock Rat was formally described as a new species in 2005.