Champasak is a province in southwestern Laos, near the borders with Thailand and Cambodia. It is one of the three principalities that succeeded the Lao kingdom of Lan Xang.

Population: 501,994 (2009 estimate). The river Mekong ceases to be the border with neighboring Thailand and, after a sharp bend projecting westward, turns east and flows southeasterly through the province down to Cambodia. The capital is Pakxe, but it takes its name from Champasak, the former capital of the Kingdom of Champasak. Champasak plays a central role in the history of Siam and Laos, with frequent battles taking place in and around Champasak.

The small town of Champasak, location of the Khmer ruins of Wat Phu, is the seat of the Champasak District. Khone Phapheng Falls is in the province. The province was the site of Laos's first railway, the Don Det – Don Khon narrow gauge railway on Don Det and Don Khon islands.

Neighboring are (from North clockwise) the provinces Salavan, Xekong and Attapu, as well as Cambodia (provinces Stung Treng and Preah Vihear) to the south and Thailand (Ubon Ratchathani Province) to the west.

Champasak can be reached from Thailand through Sirindhorn District's Chong Mek border crossing, at Vang Tao. From where the highway leads east towards the city of Pakxe. Crossing the border at Chong Mek is relatively straightforward, as there are large border posts on both sides of the border, as well as large outdoor markets.