Mühledorf is a former municipality in the Bucheggberg District, in the canton of Solothurn, Switzerland. On 1 January 2014 the former municipalities of Mühledorf (SO), Tscheppach, Brügglen, Aetingen, Aetigkofen, Bibern (SO), Gossliwil, Hessigkofen, Küttigkofen, Kyburg-Buchegg merged into the new municipality of Buchegg.