Undulatoolithus is an oogenus of Chinese fossil dinosaur egg belonging to Elongatoolithidae.

Several fossil eggs, egg clutches, and dinosaur bones were discovered, including those later described as Undulatoolithus in 2013 by Chinese paleontologists Wang Qiang, Zhao Zikui, Wang Xiaolin, Li Ning, and Zou Songlin.

The type and only known specimen of Undulatoolithus was the first elongatoolithid egg clutch discovered in the Pingxiang basin.

Like most elongatoolithids it is covered with nodes and ridges, but they are much more prominent than other oospecies and make up nearly half the total eggshell thickness.

[1] Undulatoolithus has not been associated with embryos or skeletal remains, so the identity of the egg-laying dinosaur is unknown.