QJ

QJ may refer to:
 * QJ (New York City Subway service), a defunct rapid transit service (1960–1973)
 * ATCvet code QJ (Antiinfectives for systemic use), a veterinary medication class
 * China Railways QJ, a Chinese steam rail locomotive class (built 1956–1988)
 * Quarterly Journal of Austrian Economics, since 1998, by the Mises Institute
 * Quarterly Journal of Economics, since 1886, by Harvard University
 * QJ, a UHF IMTS radio frequency