The Oinwars also known as Oinwaras were a medieval Maithil dynasty based in the Mithila region of Bihar, India. The rulers of this dynasty belonged to the Maithil Brahmin caste and the Kashyap gotra with the capital of the dynasty in the town of Sugouna in Madhubani district.

They emerged after the fall of the Karnata dynasty and ruled Mithila for roughly 200 years. Being native Maithils themselves, they are noted for patronising Maithil culture and the Maithili language.

The name Oinwar originated from the village of Oini which was obtained by Nath Thakur who was gifted it by the previous king of the region. He subsequently became known as Oini Thakur. After the fall of the previous dynasty, Oini Thakur obtained power and thus the dynasty was named the Oinwars. The rise of the Oinwars signalled the end of Rajput dominance in Mithila as all subsequent dynasties were Maithil Brahmins.

After Oini Thakur, 20 other Kings and Queens followed and the Oinwars ended up ruling Mithila until 1526. The most famous of the Oinwar line was King Shiva Singh who patronised a line of Maithili scholars including the famous Vidyapati. He ruled for 3 years and 9 months and died in a battle with Sultan Ibrahim Shah of the Jaunpur Sultanate after attempting to declare Mithilas' independence.

The scholar and poet Vidyapati, who worked in the Oinwar court gave a detailed account on the military administration. He describes the soldiers as being experts in naval combat. The military organisation was under the direct control of a Senapati or the commander-in-chief. Gandhawaria Rajputs constituted the core of the army however Chauhans and Chandelas were also mentioned. The Oinwar army imported horses of different breeds from other parts of India along with elephants and made use of various sorts of bows, arrows, spears and maces.

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