Altıeylül is a planned district and second level municipality in Balıkesir Province, Turkey. According to Law act no 6360, all Turkish provinces with a population more than 750 000, will be metropolitan municipality and the districts within the metropolitan municipalities will be second level municipalities. The law also creates new districts within the provinces in addition to present districts. These changes will be effective by the local elections in 2014.
Thus after 2014 the present Balıkesir central district will be split into two. A part will be named Altıeylül and the name Balıkesir will be 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.