The 1991 Floreat state by-election was a by-election for the seat of Floreat in the Legislative Assembly of Western Australia held on 20 July 1991. It was triggered by the resignation of Andrew Mensaros (the sitting Liberal member) on 16 May 1991, due to ill health. He died before the by-election was held. The election was won by an independent candidate, Liz Constable, who finished with 58.94 percent of the two-candidate-preferred vote. Constable became the first woman to win election to the Parliament of Western Australia as an independent (although not the first to sit as an independent – Pam Buchanan had resigned from the Labor Party earlier in the year), and only the third woman overall to win a by-election (after May Holman in 1925 and Judy Edwards in 1990).