Houayxay (Lao: ຫ້ວຍຊາຍ, pronounced [hȕaj sáːj]; Thai: ห้วยทราย, pronounced [huâj sāːj]) (also Huoeisay, Huai Sai, Houei Sai or Huay Xai), is a district in Bokeo Province, Laos, on the border with Thailand.

The town lies on the Mekong River opposite Chiang Khong in Thailand.

The Fourth Thai-Lao Friendship Bridge at Ban Houayxay, which opened in December 2013 and replaced ferry service across the river, is now the northernmost road border crossing between the two countries.

Houayxay has a domestic airport (HOE) with regular flights to Vientiane and Luang Prabang (depending on the season).

It is a series of ziplines and treehouses providing a unique overnight experience.