Phimai (Thai: พิมาย, pronounced [pʰí(ʔ).māːj]; Northeastern Thai: พิมาย, pronounced [pʰì(ʔ).ma᷇ːj]) is a district (amphoe) in the northeastern part of Nakhon Ratchasima province, northeastern Thailand.

Phimai is a lowland, making it a suitable location for settlement and agriculture. The area is fed by the Chakkarat, Khem, and Mun rivers. There is also a source of salt, which is an important resource.

Phimai is an area where evidence has been found of being the main residence of humans since the prehistoric period, approximately 1,700–3,000 years ago. These traces are still found to have continued until at least 1,500 years ago. The base of the building is made of bricks under Prasat Hin Phimai, therefore, it is assumed that it was probably originally the location of a Buddhist monastery.

Phimai was an ancient Khmer city named Vimai or Vimayapura. A stone pillar dating to the reign of King Suryavarman I was found, naming the city Bhirapura meaning 'strong city'. The rulers of Phimai during the Khmer era were all descendants of the Mahidharapura dynasty. Phimai was the important city ever since, both during Ayutthaya and Rattanakosin times.

Mueang Phimai district was established in 1900. Khun Khachit Sarakam (ขุนขจิตสารกรรม) was the first governor.

Queen Mother Sriphatcharindra (Saovabha) visited Prasat Phimai and Sai Ngam (ficus forest) in 1911. The government officers and people renovated the city for the royal visit, and named six roads to commemorate the event.

In 1940 the government renamed the district by eliminating the word mueang.

The district is divided into 12 sub-districts (tambons), which are further subdivided into 208 villages (mubans). There are two sub-district municipalities (thesaban tambons): Phimai covering parts of tambon Nai Mueang, and Rang Ka Yai the whole of tambon Rang Ka Yai. There are a further 12 tambon administrative organizations (TAO).

No.	Name	Thai name
1.	Nai Mueang	ในเมือง
2.	Samrit	สัมฤทธิ์
3.	Bot	โบสถ์
4.	Krabueang Yai	กระเบื้องใหญ่
5.	Tha Luang	ท่าหลวง
6.	Rang Ka Yai	รังกาใหญ่
7.	Chiwan	ชีวาน
8.	Nikhom Sang Ton-eng	นิคมสร้างตนเอง
9.	Krachon	กระชอน
10.	Dong Yai	ดงใหญ่
11.	Than Lalot	ธารละหลอด
12.	Nong Rawiang	หนองระเวียง