Ministry of Defence St Athan or MOD St Athan (Welsh: Maes awyr Sain Tathan), formerly known as Royal Air Force St Athan, or more simply RAF St Athan, is a large Ministry of Defence unit near the village of St Athan in the Vale of Glamorgan, southern Wales.

The base was home to the RAF No. 4 School of Technical Training throughout its life, as well as a major aircraft maintenance unit. St Athan has also been used to house British Army units, including the 1st Battalion, Welsh Guards. At one time it was home to a large collection of historical aircraft.

The only squadron to operate out of St Athan on a regular basis is the Universities of Wales Air Squadron (one of fourteen RAF University Air Squadrons), flying Grob Tutors. 2300 Squadron of the Air Training Corps is also located on the Station.

Between May 1947 and August 1973, St Athan was also home for the Administrative Apprentice Training School, which provided a 20-month training programme for boys who enlisted to become clerks or work in accounting, supply and administration, prior to posting to other RAF units for a 12-year term of service.

St Athan was the designated site for the United Kingdom's new defence training academy, but the programme was cancelled in 2010. The airfield part of the site was transferred from military to civilian control on 1 April 2019.