Bang Yai (Thai: บางใหญ่, pronounced [bāːŋ jàj]) is a district (amphoe) in the western part of Nonthaburi province, central Thailand.

The district was created in 1917 as a minor district (king amphoe) by splitting it from the districts Bang Kruai and Bang Bua Thong. In 1921 it was elevated to full district status. Originally named Bang Mae Nang, on 19 October 1930 it was renamed "Bang Yai", the original name of Bang Kruai District.

Neighbouring districts are (from the north clockwise) Sai Noi, Bang Bua Thong, Mueang Nonthaburi, Bang Kruai, and Phutthamonthon of Nakhon Pathom province.

The district is divided into six sub-districts (tambons), which are further subdivided into 66 villages (mubans). Since 2020 Bang Mae Nang has had town (thesaban mueang) status, covering most parts of tambon Bang Mae Nang. There are five townships (thesaban tambons). Bang Muang covers parts of tambons Bang Muang, Bang Len, and Sao Thong Hin; Bang Yai covers parts of tambons Bang Mae Nang, Bang Yai, and Ban Mai; Sao Thong Hin covers most parts of tambon Sao Thong Hin; Bang Len covers most parts of tambon Bang Len; and Ban Bang Muang covers most parts of tambon Bang Muang. There are a further two tambon administrative organizations (TAO) responsible for the non-municipal areas of tambons Bang Yai and Ban Mai.

No.	Name	Thai name	Villages
1.	Bang Muang	บางม่วง	15
2.	Bang Mae Nang	บางแม่นาง	15
3.	Bang Len	บางเลน	11
4.	Sao Thong Hin	เสาธงหิน	08
5.	Bang Yai	บางใหญ่	06
6.	Ban Mai	บ้านใหม่	11

Bang Yai as well as neighbouring Bang Kruai and Mueang Nonthaburi is the last natural habitat of the Alexandrine parakeet and red-breasted parakeet, a medium-sized parrot in Bangkok Metropolitan Region. They live in groups on large trees in some local temples, such as Wat Suan Yai, Wat Utthayan, Wat Ampawan, Wat Chaloem Phra Kiat Worawihan.

• amphoe.com