BEI may refer to :
- Binary ethylenimine, an inactivant used in the inactivation of the foot-and-mouth disease virus
- Business Entity Identifier, an ISO 9362 Bank Identifier Code (BIC) assigned to a non-financial entity.
- Balanced Ecology, Inc.
Bei may refer to:
- 北 (pinyin běi), a Chinese character meaning north, like in Beijing
- Bei River, the northern tributary of the Pearl River in southern China
- In mathematics, Bei is one of the Kelvin functions