Wiang Kaen (Thai: เวียงแก่น; IPA: [wīaŋ kɛ̀n]) is the easternmost district (amphoe) of Chiang Rai province, northern Thailand.

Historically, the area was Mueang Wiang Kaen, on the Ngao River.

The government separated the three tambons Muang Yai, Po, and Lai Ngao from Chiang Khong district to create a minor district (king amphoe) on 1 April 1987.

Phu Chi Fa, 1,442 m high, lies at the border with Thoeng District.

[3] The district is divided into four sub-districts (tambons), which are further subdivided into 41 villages (mubans).