J class or Class J may refer to:
- NZR J class (1874), steam locomotives operating in New Zealand from 1874 until 1935
- NZR J class (1939), steam locomotives operating in New Zealand from 1939
- WAGR J class, steam locomotives operating in Western Australia from the 1890s
- WAGR J class (diesel), diesel locomotives operating in Western Australia from the 1960s
- Victorian Railways J class (1859), main line steam locomotives operating in Victoria, Australia from 1859 to 1912
- Victorian Railways J class (1954), branch line steam locomotives operating in Victoria, Australia from 1954 to 1972
- Norfolk and Western Railway class J (1879), steam locomotives operating in the United States from 1879 until 1900
- Norfolk and Western Railway class J (1903), steam locomotives operating in the United States from 1903 until 1935
- Norfolk and Western Railway class J (1941), steam locomotives operating in the United States from 1950 until 1959
- J-class Melbourne tram
- J-class Sydney tram