Houaphanh province (Laotian: ຫົວພັນ khwɛ̌ːŋ hǔːa̯ phán; Romanization of Lao: Houaphan) is a province in eastern Laos. Its capital is Xam Neua.
Houaphanh province covers an area of . The province is bordered by Vietnam to the north, east, and southeast, Xiangkhouang province to the south and southwest, and Luang Prabang province to the west. The terrain is rugged, with dense, forested mountains forming much of the province, particularly on the western side. The main road running through the province is Route 6. The principal rivers are the Nam Ma, which flows from and into Vietnam, passing the village of Ban Muang-Et, and the Nam Sam, on which the towns of Sam Neua and Sam Tai lie.
The province is the home to the Viengxay caves, an extensive network of caves used by the Pathet Lao, and the Hintang Archaeological Park, one of the most important pre-historic sites in northern Laos, dotted with standing megaliths.
Houaphanh is one of the poorest areas of Laos, but has dramatic scenery and fine textile traditions.
The province, along with Xiangkhoang, was part of the Muang Phuan Kingdom (Vietnamese: Bồn Man) since the 14th century. Following a Vietnamese invasion in 1478 led by King Lê Thánh Tông, it became Trấn Ninh Territory of the Đại Việt Kingdom with the capital at Sầm Châu (present-day Xam Neua). The area was known as Hua Phan Tang Ha Tang Hok, 'the fifth and the sixth province", and listed by Auguste Pavie as "Hua Panh, Tang-Ha, Tang-Hoc." The provincial capital was at present-day Muong Het.
The Lê Duy Mật rebels ruled the area from 1739 to 1770. In 1802, Emperor Gia Long of the newly founded Nguyễn dynasty ceded the region to the Kingdom of Vientiane. However, in the aftermath of the Lao rebellion, Chao Nôy, the prince ruler of Muang Phuan, who earlier sided with the Siamese, was executed by the Vietnamese. Emperor Minh Mạng of Vietnam reannexed the territory in 1828.
It remained a Vietnamese outpost territory until 1893 when ownership was switched by French authorities back to Laos during the French colonial period.