ZJ may refer to:
- Zettajoule (ZJ) or zeptojoule (zJ), SI multiples of a joule
- ZJ theorem, a mathematical theorem proven by George Glauberman
- ZJ model, an automobile style used in the Jeep Grand Cherokee and the Jeep Grand Wagoneer
- an abbreviation for the Zhejiang province of China
- Zambezi Airlines IATA airline designator