Khao Yoi (Thai: เขาย้อย, pronounced [kʰǎw jɔ́ːj]) is a district (amphoe) in the northern part of Phetchaburi province, western Thailand.

The district was established in 1897 and Luang Phromsan (หลวงพรหมสาร) was assigned as the first district officer. At first named Huai Luang, the district was renamed Khao Yoi in 1903 due to the site of the district office. The name of the district comes from the limestone hill called Khao Yoi which is just off Phetkasem highway. The hill contains three caves, one of which has been converted to a cave temple with a notable reclining Buddha.

Neighboring districts are (from the north clockwise) Pak Tho of Ratchaburi province, Amphawa of Samut Songkhram province, Ban Laem, Mueang Phetchaburi, Ban Lat, and Nong Ya Plong of Phetchaburi Province.

The district is divided into 10 sub-districts (tambons), which are further subdivided into 59 villages (mubans). The sub-district municipality (thesaban tambon) Khao Yoi covers parts of tambons Khao Yoi, Sa Phang, Bang Khem, and Thap Khang. There are a further seven tambon administrative organizations (TAO) responsible for the non-municipal area.

No.	Name	Thai	Villages	Pop.
01.	Khao Yoi	เขาย้อย	07	6,873
02.	Sa Phang	สระพัง	04	3,296
03.	Bang Khem	บางเค็ม	06	3,834
04.	Thap Khang	ทับคาง	05	3,548
05.	Nong Pla Lai	หนองปลาไหล	05	2,692
06.	Nong Prong	หนองปรง	06	3,935
07.	Nong Chumphon	หนองชุมพล	07	4,605
08.	Huai Rong	ห้วยโรง	04	2,507
09.	Huai Tha Chang	ห้วยท่าช้าง	08	2,034
10.	Nong Chumphon Nuea	หนองชุมพลเหนือ	07	4,373

• amphoe.com (Thai)