Altıeylül is a new intracity district and second level municipality in Balıkesir Province, Turkey. According to Law act no 6360, all Turkish provinces with a population more than 750000, were declared metropolitan municipality. The law also created new districts within the capital city which have second level municipalities in addition the metropolitan municipality. . Altıeylül is one of them.
Thus after 2014 the present Balıkesir central district was split into two . A part was named Altıeylül and the name Balıkesir was reserved for the metropolitan municipality. (Altıeylül or 6 September was the date of recovery of Balıkesir during the Turkish War of Independence in 1922.)
There were one town and 80 villages in Altıeylül rural area. Now their official status became "neighborhood of Altıeylül".As of 2013 the population of Altıeylül was Karesi was 170,260.