J4

J4/J04, J-4/J-04 or J.4/J.04 may refer to:

; In science and academia :

* ATC code J04, a class of medications used to treat leprosy and tuberculosis
* Janko group J4, in mathematics
* S/2003 J 4, a natural satellite of Jupiter
* J04 : acute laryngitis and tracheitis ICD-10 code

; In military :

* Mikoyan-Gurevich MiG-15, Chinese designation of this Soviet-made aircraft is "J-4"
* HMAS J4, an Australian Royal Navy submarine which saw service during World War I
* Junkers J 4, a 1917 German sesquiplane format warplane
* J4F was the U.S. Navy's designation for the Grumman Widgeon seaplane.

; In transportation :
* Auster J-4, a 1946 British single-engined two-seat high-wing touring monoplane
* County Route J4 (California), a road in the United States
* GS&WR Class J4, a Great Southern and Western Railway
* Malaysia Federal Route J4, a major road in Johor, Malaysia
* Piper J-4, a 1939 trainer aircraft
* Buffalo Airways International Air Transport Association code