Mongolostegus (meaning "Mongolian roof") is a genus of stegosaur from the Early Cretaceous (Aptian-Albian) Dzunbain Formation of Mongolia.

The type and only species is M. exspectabilis,[1] known from a single specimen previously under the nomen nudum Wuerhosaurus mongoliensis.

[2] Mongolostegus is one of the youngest known stegosaurs, along with Stegosaurus,[3] Yanbeilong,[4] and an unnamed species from the Dzunbain Formation.

[1] The holotype is PIN 3779-15, which consists of posterior dorsal and anterior caudal vertebrae as well as pelvic material.

[1] It was discovered in a layer of the Dzunbain Formation at Chamrin-Us, Mongolia.