Quercus cornelius-mulleri is a bushy shrub not exceeding 3 meters (10 feet) in height. It is densely branched, its tangled twigs gray, brown, or yellowish, fuzzy when new and becoming scaly with age.[8]
The evergreen leaves are leathery and thick. They are bicolored: dull gray or yellow-green and faintly hairy on the upper surfaces, and white and quite woolly on the undersides. The wool on the undersides of the leaves is made up of star-shaped leaf hairs that are fused into microscopic plates.[6] The leaf blades are oval with smooth or toothed edges, and measure 2.5 to 3.5 centimetres (1 to 1+1⁄2 inches) in length.[8]
The fruit is an acorn with a cap up to 2 cm (3⁄4 in) wide covered in light-colored scales and a cylindrical, round-ended nut up to 3 cm (1+1⁄4 in) long.[8]