Quercus peninsularis, common name peninsular oak, is a species of oak endemic to Baja California, Mexico. It is a shrub or small tree to 10 m, occurring in mountain valleys and canyons up to 3000 m. It is classified as a red oak (section Lobatae). Leaves are 5–8 cm, flat, leathery and hairy, with pointed tips and 2-5 pairs of teeth. Flowers occur in 3 cm catkins. Fruits are 1.5 cm acorns, stemless, ovoid, with hairy cupules, maturing in a year. Mature bark is reddish; young twigs are thin and hairy.