Ilex mitis is an evergreen tree, between 10 and 25 m tall, with a straight trunk and a rounded canopy. Stems are normally round. Bark on the young tree is a pale grey-brown with patches of white, smooth with fine, transverse ridges and yellow-brown corky specks. As the tree becomeslder it becomes evenly whitish-grey with dark rough spots.

Young twigs are a reddish purple colour. The simple lance-shaped alternate leaves are a shiny dark green and are carried on plum-coloured stalks. They are between 70-100 x 19-25 mm, with pointed, sometimes curled tips and wavy, sometimes slightly toothed margins. The plum-coloured leaf stalks help to identify the tree. The midrib is sharply impressed above and prominent below.

The small flowers are borne in spring or early summer in bunches between the leaf axils. They are white and sweetly scented. Male and female flowers are borne on separate trees. The forest floor below the trees become carpeted with tiny, white flower petals that are shed as the fruit begins to develop.

Fruits ripen on the female trees in autumn, turning bright red, and as these are densely packed along the stems, they provide bright splashes of colour, attracting many kinds of birds. There are several seeds in each fruit which is small and round with a sharp point. Fruiting trees are conspicuous when viewed from above.

The wood is whitish to grey-green, is close-grained, medium-hard and medium-heavy and is easily worked.