Østergaard () is a Danish surname, literally meaning east farm. The double a "aa" is equivalent of å in common nouns and is retained from the pre-1948 orthography in proper nouns only. Notable people with this surname include:
Østergaard Flemming Østergaard (born 1943), Danish businessman Morten Østergaard (born 1976), Danish politician Niki Østergaard (born 1988), Danish road racing cyclist Søren Østergaard (born 1957), Danish film, television and stage actor Ulrich Østergaard (born 1981), Danish speedway rider
Ostergaard Geoffrey Ostergaard (1926–1990), political scientist and anarcho-pacifist Henrik Ostergaard (1968–2011), Danish-born guitarist/vocalist and founder of rock band Dirty Looks