Llanuwchllyn (Welsh: [ɬaˈnɨ̞u̯χɬɨn] ⓘ) is a village and community in Gwynedd, Wales, near the southern end of Bala Lake (Llyn Tegid).

The village was the birthplace of Welsh language author and educationalist Owen Morgan Edwards.

Caer Gai, a Roman fort near Llanuwchllyn, was traditionally known as the home of Cei, the character in the Arthurian legend known in English as Sir Kay.

Poets of the 15th century recorded a story, ultimately deriving from the Prose Merlin included in the Lancelot-Grail and the Post-Vulgate Cycle, that King Arthur and Cei were brought up at Caer Gai as foster brothers.

[3] According to the 2011 Census, Llanuwchllyn is the community with the 2nd highest percentage of Welsh speakers in Wales.