Nanotyrannus (nan-oh-tie-ran-us) is a genus of dinosaur. It was erected in 1988 for a small tyrannosaurid skull, previously described in 1946 (Gilmore) as Albertosaurus lancensis.

Initial research indicated that the skull bones were fused, and that it therefore represented an adult specimen. Nanotyrannus was a bipedal meat-eater, a theropod from the late Cretaceous Period (68-65 million years ago). It was about 16 feet long (5 metres), had a large head, long legs with three-toed feet, short arms with two-fingered hands, a short, thick neck, large jaws with sharp teeth, narrow hips, and a slim tail.