SAO or S.A.O. may stand for:
- Saco Transportation Center (Amtrak station code SAO), a train station in Saco, Maine, United States
- Session-At-Once, a recording mode for optical discs.
- Smithsonian Astrophysical Observatory of the Smithsonian Institution in Cambridge, Massachusetts
- Smithsonian Astrophysical Observatory Star Catalog
- Special Astrophysical Observatory of the Russian Academy of Science, the site of the BTA-6 Telescope, which for many years was the world's largest telescope
- Security Advisory Opinion, a decision-making process used by the US Department of State and United States embassies to grant or deny United States visas
- SAO, the ICAO airline designator for the Sahel Aviation Service airline
- SAO, the IATA airport code for airports in the São Paulo Metropolitan Area, Brazil
- Sword Art Online, Japanese light novel, manga and anime series by Reki Kawahara.
- Shin Angyō Onshi, manga-manhwa and animated film created by Youn In-wan and illustrated by Yang Kyung-il.
- ^ Airline codes-All
- ^ Airline codes-S
- ^ List of airports by ICAO code: S
- ^ Campo de Marte Airport - Sao Paulo, Brazil