Sao may refer to:
- Sao language, an aboriginal language of Taiwan
- Sao, Burkina Faso
- The Sao civilisation who lived south of Lake Chad
- The Sáo, a bamboo transverse flute used in Vietnam
- Sao (moon) of Neptune
- Sao, one of the Nereids
- São, the Portuguese word for saint. It is also a common abbreviation of the given name Conceição.
- SAO biscuits, produced by Arnott's
- Sao (trilobite), a genus of ptychopariid trilobite
- Sao, nickname of the Chad national football team
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 series by Reki Kawahara.