4J

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