The Battle of Poimanenon or Poemanenum was fought in early 1224 (or possibly late 1223) between the forces of the two main successor states of the Byzantine Empire; the Latin Empire and the Byzantine Greek Empire of Nicaea. The opposing forces met at Poimanenon, south of Cyzicus in Mysia, near Lake Kuş.

Summing up the importance of this battle, the 13th-century Byzantine historian George Akropolites wrote that "Since then (this battle), the state of the Italians [the Latin Empire] ... began to decline".

The news about the defeat at Poimanenon caused panic in the Latin imperial army besieging Serres from the Despotate of Epirus, which withdrew in chaos in the direction of Constantinople and was therefore defeated decisively by the troops of the Epirote ruler, Theodore Komnenos Doukas. This victory opened up the way for the recovery of most of the Latin possessions in Asia. Threatened both by Nicaea in Asia and Epirus in Europe, the Latin emperor sued for peace, which was concluded in 1225. According to its terms, the Latins abandoned all their Asian possessions except for the eastern shore of the Bosporus and the city of Nicomedia with the surrounding region.