| Official Name: | Mae Chai |
| Native Name: | แม่ใจ |
| Native Name Lang: | th |
| Settlement Type: | District |
| Subdivision Type: | Country |
| Subdivision Name: | Thailand |
| Subdivision Type1: | Province |
| Subdivision Name1: | Phayao |
| Subdivision Type2: | Seat |
| Subdivision Name2: | Si Thoi |
| Subdivision Type3: | Subdistricts |
| Subdivision Name3: | 6 |
| Subdivision Type4: | Mubans |
| Subdivision Name4: | 65 |
| Established Title: | District established |
| Population Total: | 36089 |
| Population As Of: | 2005 |
| Blank Name Sec1: | Postal code |
| Blank Info Sec1: | 56130 |
| Blank Name Sec2: | Geocode |
| Blank Info Sec2: | 5607 |
| Timezone: | ICT |
| Utc Offset: | +7 |
| Coordinates: | 19.345°N 99.815°W |
Mae Chai (Thai: แม่ใจ, in Thai pronounced as /mɛ̂ː tɕāj/; แม่ใจ๋, pronounced as /mɛ̂ː tɕǎj/) is a district (amphoe) of the Phayao province in northern Thailand.
The District Mae Chai was abolished on 23 December 1917 and was incorporated into Mueang Phan district.[1] It was recreated as a minor district (king amphoe) on 24 January 1963.[2] It was upgraded to a full district on 28 July 1965.[3] In 1977 the district was reassigned from Chiang Rai Province to the newly established Phayao Province.
The district is in the upper valley of the Ing River. West of the town Mae Chai is the 1,426 m high Doi Luang mountain of the Phi Pan Nam Range. It rises within a protected area in the Doi Luang National Park. To the east is the Nong Liang Sai Reservoir, and at the boundary to the Mueang District the Mae Pim Reservoir. Mae Puem National Park protects the Mae Puem National Conserved Forest and Dong Pradu Forest.
Neighboring districts are (from the north clockwise): Phan and Pa Daet of Chiang Rai province; Mueang Phayao of Phayao Province; and Wang Nuea of Lampang province.
The district is divided into six sub-districts (tambons), which are further subdivided into 65 villages (mubans). The township (thesaban tambon) Mae Chai covers parts of tambons Mae Chai and Si Thoi. There are a further six tambon administrative organizations (TAO).
| No. | Name | Thai name | Villages | Pop. | ||
|---|---|---|---|---|---|---|
| 1. | Mae Chai | แม่ใจ | 10 | 5,094 | ||
| 2. | Si Thoi | ศรีถ้อย | 13 | 7,267 | ||
| 3. | Mae Suk | แม่สุก | 10 | 5,830 | ||
| 4. | Pa Faek | ป่าแฝก | 10 | 5,538 | ||
| 5. | Ban Lao | บ้านเหล่า | 14 | 8,219 | ||
| 6. | Charoen Rat | เจริญราษฎร์ | 8 | 4,141 |