Wannanosaurus is a genus of dinosaur belonging to the family Pachysephalosauridea. It lived approximately 70 to 66 million years ago during the Late Cretaceous period in what is now China. The first fossils of Wannanosaurus were discovered in the late 20th century

It is known from a single partial skeleton, which includes a partial skull roof and lower jaw, a femur and tibia, part of a rib, and other fragments. Due to its flat skull roof with large openings, it has been regarded as primitive among pachycephalosaurs.

Despite its remains being from a very small individual, with a femur length of approximately 8 centimeters (3.1 inches) and an estimated overall length of about 60 cm (2 ft), the fused bones in its skull indicate that it was an adult at the time of its demise. Like other pachycephalosaurians, it likely had a herbivorous or omnivorous diet, feeding on a variety of plant matter close to the ground, possibly supplemented with insects.