Abstract: A new thalattosaurian, Miodentosaurus brevis gen. et sp. nov., is established on the basis of the fairly preserved skull and mandible of a skeleton from the Triassic Falang Formation, Guizhou Province. M. brevis is a relatively large thalattosaurian, with a total length of more than 4 m. The very short snout, with a straight profile, is the most striking of the diagnostic characters of the new taxon. Other diagnostic features include the presence of a crest along the anterodorsal midlines of the premaxillae, the edentulous maxilla, the presence of a groove-like trough along with the anterolateral margin of the maxilla on the ventral surface, the presence of six conical premaxillary teeth, and no more than six conical dentary teeth which are restricted to the anterior portion of the dentary. The absence of the vomer and pterygoid teeth, the anterior shift of the large pineal foramen, and the elongation of the neck indicate that M. brevis may have had a close relationship with the Askeptosauroidea, to which the Chinese genus, Anshunsaurusis referred.