| Official Name: | Lan Sak |
| Native Name: | ลานสัก |
| Native Name Lang: | th |
| Settlement Type: | District |
| Subdivision Type: | Country |
| Subdivision Name: | Thailand |
| Subdivision Type1: | Province |
| Subdivision Name1: | Uthai Thani |
| Subdivision Type2: | Seat |
| Subdivision Name2: | Lan Sak |
| Subdivision Type3: | Tambon |
| Subdivision Type4: | Muban |
| Established Title: | District established |
| Population Total: | 57548 |
| Population As Of: | 2005 |
| Blank Name Sec1: | Postal code |
| Blank Info Sec1: | 61160 |
| Blank Name Sec2: | Geocode |
| Blank Info Sec2: | 6107 |
| Timezone: | ICT |
| Utc Offset: | +7 |
| Coordinates: | 15.4528°N 99.5761°W |
Lan Sak (Thai: ลานสัก, in Thai pronounced as /lāːn sàk/) is a district (amphoe) in northern Uthai Thani province, northern Thailand.
Tambons Lan Sak and Pradu Yuen of Ban Rai district were combined as a minor district (king amphoe) on 15 October 1975.[1] The minor district office was in Ban Pak Muean. It was upgraded to a full district on 13 July 1981.[2] At the same time, the office was moved to Ban Kao.
Neighboring districts are (from the east clockwise) Sawang Arom, Thap Than, Nong Chang, Huai Khot, and Ban Rai of Uthai Thani Province; Mae Poen and Chum Ta Bong of Nakhon Sawan province.
The important water resources are the Huai Thap Salao reservoir and Kha Khaeng River (Huai Kha Khaeng).
The district is divided into six sub-districts (tambons), which are further subdivided into 81 villages (mubans). The township (thesaban tambon) Lan Sak covers parts of tambons Lan Sak and Pradu Yuen. There are a further six tambon administrative organizations (TAO).
| No. | Name | Thai name | Villages | Pop. | ||
|---|---|---|---|---|---|---|
| 1. | Lan Sak | ลานสัก | 10 | 13,905 | ||
| 2. | Pradu Yuen | ประดู่ยืน | 12 | 6,697 | ||
| 3. | Pa O | ป่าอ้อ | 10 | 7,358 | ||
| 4. | Rabam | ระบำ | 19 | 12,573 | ||
| 5. | Nam Rop | น้ำรอบ | 18 | 9,635 | ||
| 6. | Thung Na Ngam | ทุ่งนางาม | 12 | 7,380 |
Hup Pa Tat is a broad valley located in the north of Uthai Thani Province.