Mae Chai is a small town and subdistrict (tambon) located in the Mae Chai District of Phayao Province, Thailand. Situated in the northwestern part of the province near the border with Lampang Province, it serves as the principal town of its district. The area is shared with tambon Si Thoi and consists of 10 villages.
The town lies along National Road 1, which connects it to Phayao in the south and leads toward Pa Faek and Mae Yen in Chiang Rai Province to the north. Geographically, the subdistrict is situated partly within Mae Puem National Park and is traversed by the Mae Chai River.