Sio or SIO may refer to:

Places Sió, an artificial channel in Hungary Siø, a small Danish island in the South Funen Archipelago Sio, Burkina Faso, a village in Burkina Faso Sio, Mali, a commune in Mali Sio, Papua New Guinea, a town in Papua New Guinea Sio, a river in Western Africa providing water for the Lake Togo Smithton Airport (IATA airport code), Tasmania, Australia

Computing Atari SIO, a peripheral bus Super I/O, a motherboard chipset component Start I/O (SIO) instruction on IBM S/360 or S/370.

Organizations Scripps Institution of Oceanography, La Jolla, California, U.S. Students Islamic Organisation of India Foundation for Student Life in Oslo (Studentsamskipnaden i Oslo) Sexarbejdernes Interesse Organisation, a Nordic organization of sex workers (see Prostitution in Sweden)

People Sio (cartoonist), Italian comics artist William Sio (born 1960), New Zealand politician David Sio (born 1962), Samoan rugby union footballer Giovanni Sio (born 1989), Ivorian international footballer Ken Sio (born 1990), Australian rugby league player Michael Sio (born 1993), New Zealand rugby league player

Other uses Battle of Sio, part of the New Guinea campaign of World War II ISO 639:sio or Siouan, a language family of North America Sio language, an Austronesian language Sio (fish), a genus of fish SiO, the chemical formula for Silicon monoxide SiO2, the chemical formula for Silicon dioxide Senior Investigating Officer, the lead officer in a criminal investigation in the U.K.

See also De Sio, a surname