Oudomxay is a province of Laos, located in the northwest of the country. The province capital is Muang Xai.

Oudomxay Province covers an area of 15,370 square kilometres (5,930 sq mi). The province borders China to the north, Phongsali Province to the northeast, Luang Prabang Province to the east and southeast, Xaignabouli Province to the south and southwest, Bokeo Province to the west, and Luang Namtha Province to the northwest. The topography of Oudomxay is mountainous, between 300–1,800 metres (980–5,910 ft) above sea level.

Oudomxay has deposits of salt, bronze, zinc, antimony, brown coal, kaolin and iron deposits. Attempts to control poppy cultivation in the province have been made through the Narcotics Crop Control Project, formulated in the 1990s. Besides rice, important crops are corn, soybeans, fruits, vegetables, cassava (maniok), sugarcane, tobacco, cotton wool, tea and peanuts. In 2004, approximately 10,000 tons of sugarcane and 45,000 tons of corn were produced.