Ban Houayxay (Lao: ຫ້ວຍຊາຍ) (also known as Huay Xai, Houei Sai etc.) is the capital of the Lao province of Bokèo, on the border with Thailand.

The town lies on the Mekong river opposite Chiang Khong in Thailand being the northernmost border crossing between the two countries. The two are only connected via ferries. Houayxay is also the endpoint of national road no. 3 which connects China via the border at Boten in Yunnan province and Luang Namtha with Thailand. A bridge to Thailand is scheduled for completion in 2012.

Houayxay has a domestic airport with regular flights to Vientiane (capital of Laos) and Luang Prabang (depending on the season). Probably the most popular means of transport are boats (speed and slow boats, freighters, luxury cruisers for tourists and others) running down the Mekong to Pakbeng, Luang Prabang and other destinations.

Fort Carnot, an ancient French fort in ruins, is situated on a hill overlooking the town and the Mekong river.

Coordinates: 20°17′N 100°25′E / 20.283°N 100.417°E / 20.283; 100.417