Catherine Sarah Deakin (also known as Katie and Kate) (1850–1937) was an Australian music teacher and pianist.

[2] Deakin taught piano and music theory privately, including to her brother Alfred's daughters, Ivy, Vera and Stella.

Historian Marjorie R. Theobald described Deakin as the most important person in Alfred's life.

She advised Alfred on political and intellectual matters, influencing his role as Australian prime minister.

She travelled regularly with the girls, accompanying them to Berlin and Budapest for studies.