4J or 4-J may refer to:
- 4J Studios, a Scottish video game developer
- Somon Air's IATA code
- Eugene School District's designator
- 4J Road, a section of Wyoming Highway 50
- 4J, the production code for the 1975 Doctor Who serial The Android Invasion
In aircraft:
- TA-4J, a model of Douglas A-4 Skyhawk
- F-4J Phantom, see McDonnell Douglas F-4 Phantom II
- F-4J Phantom II, see List of McDonnell Douglas F-4 Phantom II variants
- F-4J(UK), see McDonnell Douglas F-4 Phantom II non-U.S. operators
- L-4J, a model of Piper J-3