The Battle of Siauliai or Battle of the Sun (Lithuanian: Saules Musis) took place on September 22,1236 near the town of Siauliai, which today lies in the region of Joniskis, Lithuania. The "Chronicum Livonae" by Herman de Wartberge says that battle was fought in "terram Sauleorum", but it's not proved that "terram Sauleorum" is Siauliai.

The knights of the Livonian Brothers of the Sword, led by Volquin were defeated by the Zemaiciai, a Lithuanian ethnic group inhabiting the region called Samogitia. The Zemaiciai were led by duke Vykintas. After this battle the Livonian Brothers of the Sword became part of the Teutonic Order.