The coloration of the upper parts ranges from pale buff through yellow fawn to brownish gray. The dorsal surface is usually darker than the sides of the body, and the sides of the face are generally grayish. The underparts are white. The tail is generally brown, the hands and feet are pale grayish or white, and the scantily haired ears have a reddish tinge. Thallomys is characterized by its long tail and short feet.
Females have three pairs of mammae.
As the common name suggests, this rodent is usually associated with acacia trees, where it nests in forks or branches, in crevices in the trunk, in hollow limbs, under loose bark, or in holes in the ground at the base of the tree. The nests are built of twigs and other vegetable matter. It is an expert climber but occasionally will drop to the ground in an effort to escape danger. It normally emerges from its retreat in the early evening to search for food. Buds and leaves are staples and are eaten in the canopy, gum is gnawed directly off the bark, and acacia and grass seeds are foraged for on the ground beneath the trees.