Olive Mary Hilliard (née Hillary, 4 July 1925 – 30 November 2022) was a South African botanist and taxonomist.

She worked at the National Herbarium in Pretoria in 1947-48 and was a lecturer in botany at Natal University from 1954 to 1962.

Her special fields of interest were the flora of Natal and the taxonomy of Streptocarpus, Compositae and Scrophulariaceae.

In 1964 she formed a professional and personal collaboration with Brian Laurence Burtt (1913-2008) who played a large part in the revitalising of a moribund Royal Botanic Garden Edinburgh.

Their collaboration resulted in numerous papers and three books, Streptocarpus: an African Plant Study (1971), The Botany of the Southern Natal Drakensberg (1987), and Dierama: The Hairbells of Africa (1991).