Altıeylül is a municipality and district of Balıkesir Province, Turkey. Its area is 956 km, and its population is 183,736 (2022).
The district was established in 2012, when Balıkesir Province was declared a metropolitan municipality as a part of the 2013 Turkish local government reorganisation (Law no. 6360). Altıeylül was created out of the former Balıkesir central district, along with Karesi. The name Altıeylül means "6 September", which was the date of recovery of Balıkesir during the Turkish War of Independence in 1922.