Acacia brockii is a tree belonging to the genus Acacia and the subgenus, Phyllodineae, in the family Fabaceae, and is endemic to the Northern Territory.
Acacia brockii is a slender tree growing to 5 metres, with silvery-grey foliage.
Acacia brockii is distinguished from other Northern Territory Acacias by its flattened hairs on its phyllodes which fall off, its fringed bracteoles with acute apices which extend beyond the flower buds, and by the fine, long, silvery hairs on its calyces.
The type specimen was collected in Kakadu National Park on April 21, 1990 by A.V. Slee & L.A. Craven (#2694), with holotypes, NSW 236231, MEL 1617292A, PERTH 3347060 and elsewhere.
The specific epithet, brockii, honours John Brock, the Northern Territory author and botanical consultant who first collected this species.