U4, U-4, or U04 may refer to:
Science and technology U4 spliceosomal RNA, a non-coding RNA component of the major U2-dependent spliceosome Haplogroup U4 (mtDNA), a human genetic group U4, unitary group of degree 4 U-47700, a synthetic opioid U04, the ICD-10 code for severe acute respiratory syndrome
Transport U-Bahn lines U4 (Berlin U-Bahn) U4 (Frankfurt U-Bahn) U4 (Hamburg U-Bahn) U4 (Munich U-Bahn) U4 (Vienna U-Bahn) German submarine U-4, one of several German submarines London Buses route U4 U-4, the U.S. Air Force version of the Aero Commander (aircraft), a light twin-engined aircraft from Aero Design and Engineering Company U-4, the Japanese air self-defense force designation for the Gulfstream IV aircraft U4, PMTair (former) IATA airline designator U4, Buddha Air current IATA airline designator
Other uses U4, the former name of the Maple League of Universities U4, an unemployment figure released by the United States Bureau of Labor Statistics Ultima IV: Quest of the Avatar, a video game U4 Anti-Corruption Resource Centre en organisasjon under
See also 4U (disambiguation)