Olaf Hagerup (29 September 1889 – 2 March 1961) was a Danish botanist. He studied botany at the University of Copenhagen from 1911 under the professors Eugenius Warming, Christen C. Raunkiær, L. Kolderup Rosenvinge og W. Johannsen. He took his Ph.D. from the same university in 1930. From 1934 to 1960, he was superintendent at the Botanical Museum of the University of Copenhagen. The standard author abbreviation Hagerup is used to indicate this person as the author when citing a botanical name.