Nong Ya Sai (Thai: หนองหญ้าไซ, pronounced [nɔ̌ːŋ jâː sāj]) is a district (amphoe) in the western part of Suphan Buri province, central Thailand.

The minor district (king amphoe) was created on 1 June 1983, when the four tambons Nong Ya Sai, Nong Rathawat, Nong Pho, and Chaeng Ngam were split off from Sam Chuk district.

[2] Neighboring districts are (from the north clockwise) Dan Chang, Doem Bang Nang Buat, Sam Chuk, and Don Chedi of Suphan Buri Province, and Lao Khwan of Kanchanaburi province Nong Ya Sai is divided into six sub-districts (tambons), which are further subdivided into 66 administrative villages (mubans).

There is one sub-district municipality (thesaban tambon) in the district: There are six sub-district administrative organizations (SAO) in the district:

This Suphan Buri Province location article is a stub.