Si Wilai is a subdistrict (tambon) located in the Si Wilai District of Bueng Kan Province in northeastern Thailand. It serves as the administrative seat of the Si Wilai District.
The area lies along Thailand Route 222, situated south of Non Sombun and Bueng Kan. As of 2010, the subdistrict had a population of 10,846 people and held jurisdiction over 12 villages. Public transportation to the area is facilitated by a bus service connecting Si Wilai to Bueng Kan.