UJ may stand for:
- Jagiellonian University of Kraków, Poland
- Union Jack (correctly known as the Union Flag)
- Universal joint
- Uditha Jayawardena
- University of Jaffna
- University of Johannesburg
- University of Jordan, the oldest institution of higher learning in Jordan
- University of Judaism, the former name of the American Jewish University
- Microjoule (μJ), unit of measure, one millionth of one joule