In Irish mythology, Naisi, Noíse or Noisiu (modern spelling: Naoise [ˈn̪ˠiːʃə]) was the nephew of King Conchobar mac Nessa of Ulster, and a son of Uisneach (or Uisliu). He is mentioned in the tale known as the Tragic Tale of the Sons of Uisnech, or Exiles of the Sons of Uisnech, usually found within the set of stories in the Táin Bó Cúailnge, part of the Ulster Cycle.

In the tale he becomes the lover of Deirdre, a woman of great beauty, who is also desired by the king of Ulster Conchobar mac Nessa - as a consequence the lovers with Naoise's two brothers go into exile in Scotland (Alba). Eventually, Conchobar seeks to get them to return, but a series of unfortunate events (including a geas placed on Fergus mac Róich their protector and escort, as well as Naoise and his brothers' repeated disregard for Deirdre's prophetic warnings) and the treachery of Conchobar brought on by his desire for Deirdre, leads to tragedy.

The tale climaxes with battle at the Red Branch house at Emain Macha, with many dead including Naoise, his brothers Ainle and Ardan, and Conchobar's son Fiacha. Ultimately the sons of Uisnech are killed in one blow delivered by Maine Red Hand son of the King of Norway (or by Éogan mac Durthacht depending on source). The whole event leads to considerable strife between Ulster and Connacht, the disinheritance of Conchobar and his descendants to the title King of Ulster, and the destruction of Emain Macha.