SIAT may refer to:
- S.I.A.T. (Sociedad Ibérica de Automóviles de Turismo), the predecessor company of the Spanish car maker SEAT (S.E.A.T., Sociedad Española de Automóviles de Turismo)
- Siebelwerke/ATG, a German aircraft manufacturer
- Sibaviatrans, a Russian airline
- N-acetyllactosaminide alpha-2,3-sialyltransferase, an enzyme