QJ may mean:
- QJ, a defunct line on the New York City Subway, now called the J-Z (New York City Subway service)
- QJ, a UHF band frequency - see IMTS Frequencies
- China Railways QJ, a Chinese 2-10-2 steam locomotive
- Quarterly Journal of Economics
- Quarterly Journal of Austrian Economics
- ATCvet code QJ Antiinfectives for systemic use, a section of the Anatomical Therapeutic Chemical Classification System for veterinary medicinal products