A by-election was held for the Australian House of Representatives seat of Kalgoorlie on 18 December 1920. It was triggered by the expulsion from the House of Labor Party MP Hugh Mahon. The subsequent by-election was won by Nationalist Party candidate George Foley. It is the only federal by-election in Australian history at which the government has won a seat from the opposition. Voting was not compulsory in 1920.