Abstract: We report on a new species of basal ornithuromorph bird,Tianyuornis cheni gen. et sp. nov., based on a nearly complete and articulated subadult individual from the Lower Cretaceous Yixian Formation in the eastern region of Nei Mongol, China. The new specimen shows features characteristic of the Hongshanornithidae (Hongshanornis longicresta,Longicrusavis houi, and Parahongshanornis chaoyangensis), such as small body size and elongate hindlimbs relative to their forelimbs, but it also possesses some unique features that support the erection of a new genus and species, including a straight dentary (a sigmoidal dentary was previously considered an autapomorphy of hongshanornithids), teeth preserved on both the upper and lower jaws, sternal caudolateral trabecula has a distinct fan-shaped expanded distal end. With the addition of this new taxon, Hongshanornithidae represents the most diverse recognized clade of Early Cretaceous ornithuromorphs. The new specimen reveals new important morphological information regarding the Hongshanornithidae and confirms the controversial presence of teeth in this clade.