Khai Si (Thai: ไคสี) is a subdistrict (tambon) in Mueang Bueng Kan district, in Bueng Kan province, Isan (northeastern Thailand).

As of 2022, it had a population of 5,466 people and has jurisdiction over ten villages.

[1] It lies on Highway 212 and the Mekong River and border with Laos, west of Bueng Kan and east of Ho Kham.

[3] The administration of Khai Si subdistrict (tambon) is responsible for an area that covers 36,905 rai ~ 59.04 square kilometres (22.80 sq mi) and consists of ten administrative villages (muban).

Khai Si subdistrict is home to the following active temples, where Theravada Buddhism is practised by local residents:[5]