Simple Summary The superfamily Cercopoidea is commonly named as "spittlebugs", as its nymphs excrete a spittle mass to protect themselves and hide from predators and parasites. Cosmoscartini (Cercopoidea: Cercopidae) is a large and brightly colored Old World tropical tribe, including 11 genera. A new genus Nangamostethos gen. nov. (type species: Nangamostethos tibetense sp. nov.) of Cosmoscartini is described from Niubao Formation, the late Eocene (ca. 39 million years ago) of central Tibetan Plateau (TP), China. Its placement is ensured by comparison with all the extant genera of the tribe Cosmoscartini. The new fossil represents one of the few fossil Cercopidae species described from Asia. It is likely that Nangamostethos was extinct from the TP due to the regional aridification and an overturn of plant taxa in the last 33 million years. The superfamily Cercopoidea is commonly named as "spittlebugs", as its nymphs produce a spittle mass to protect themselves. Cosmoscartini (Cercopoidea: Cercopidae) is a large and brightly colored Old World tropical tribe, including 11 genera. A new genus Nangamostethos gen. nov. (type species: Nangamostethos tibetense sp. nov.) of Cosmoscartini is described from Niubao Formation, the late Eocene of central Tibetan Plateau (TP), China. Its placement is ensured by comparison with all the extant genera of the tribe Cosmoscartini. The new fossil represents one of few fossil Cercopidae species described from Asia. It is likely that Nangamostethos was extinct from the TP due to the regional aridification and an overturn of plant taxa in the late Paleogene.