Officer Cadet Training Unit or OCTU may refer to one of a number of former military establishments for training future commissioned officers of the British Army, the British Indian Army, and the Royal Air Force.
British Army
- 102 (Westminster Dragoons) Officer Cadet Training Unit (TA), was at Westminster
- 133 (AA) Officer Cadet Training Unit was at Shrivenham during the Second World War and trained cadets in Anti-Aircraft work
- 161 Infantry Officer Cadet Training Unit (RMC), established in 1939, later became the Mons Officer Cadet Training Unit (Aldershot), which in 1960 was merged into the Mons Officer Cadet School.
- Eaton Hall Officer Cadet Training Unit was at Eaton Hall, Cheshire; in 1960, it was also merged into the Mons Officer Cadet School.
- 162 Officer Cadet Training Unit was formed in 1939 from the Infantry Battalion of the Honourable Artillery Company; it was at Lanark, Scotland, in 1942, and later became part of the York OCTU (previously No. 103)
- 163 Officer Cadet Training Unit was formed during the Second World War from the Artists Rifles
- 165 Officer Cadet Training Unit existed during the Second World War at Lauderdale House, Dunbar.
- The Royal Armoured Corps Officer Cadet Training Unit was at the Royal Military College, Sandhurst, from 1944 to 1945
British Indian Army
- An Officer Cadet Training Unit was at Bangalore.
Royal Air Force
- No. 1 Officer Cadet Training Unit was based at RAF Millom and later at RAF Jurby and RAF Feltwell
- No. 2 Officer Cadet Training Unit was at RAF Kirton in Lindsey
- The RAF Officer Cadet Training Unit, at RAF Henlow from 1965 to 1980, then merged with the Royal Air Force College Cranwell
- Another Officer Cadet Training Unit was at RAF Spitalgate
- A Women's Royal Air Force Officer Cadet Training Unit was at RAF Henlow.