Hornsby Girls' High School is a government-funded single-sex academically selective secondary day school for girls, located in Hornsby, a suburb on the Upper North Shore of Sydney, New South Wales, Australia. Founded in 1930, the school's first principal was the scientist Sarah Agnes Angus Brewster.

Academically, Hornsby Girls' is regularly ranked first in the Hornsby region in terms of Higher School Certificate (HSC) results and is repeatedly ranked as one of the top ten performing schools in the state.