This is a list of abolished upper houses of bicameral legislatures and parliaments at national and lower levels of government. The reasons for abolition include removal of unelected houses, under-representation of ethnic/religious minorities, under-representation of women, cost-cutting in government expenditure, longer and unlimited terms in office (leading to accusations of monarchism), and to speed up the process of legislation due to upper house scrutiny.
The Legislative Council of Queensland was the upper house of the Parliament of Queensland and was entirely appointed by the Governor of Queensland. The Labor Government of Ted Theodore made the necessary appointments, and on 27 October 1921, the Legislative Council voted itself out of existence. All other Australian states continue to have bicameral systems.
Some Canadian provinces once possessed upper houses, but abolished them to adopt unicameral systems. Newfoundland had a Legislative Council prior to joining Canada, as did Ontario when it was Upper Canada. Newfoundland has the power to re-establish its upper house, the Legislative Council, pursuant to Term 14 (2) of the Terms of Union. Manitoba had an upper chamber until it was abolished in 1876, New Brunswick's upper chamber was abolished in 1892, Prince Edward Island's upper chamber was abolished in 1893, Nova Scotia's upper chamber was abolished in 1928 and Québec's upper chamber was abolished in 1968.
According to the 1938 Constitution, the Riigikogu had two chambers, which replaced the unicameral system. The lower chamber was called Riigivolikogu and the upper chamber was named Riiginõukogu. Both chambers were disbanded in 1940, following the Soviet occupation, and rigged elections for only the lower chamber Riigivolikogu were held. According to the 1992 Constitution of Estonia, the parliament is once again unicameral.
The Vidhan Parishad or Legislative Council is the upper house of the state legislature in India. The states of West Bengal, Punjab and Tamil Nadu abolished the Vidhan Parishad in their legislatures. The Vidhan Parishad of Andhra Pradesh was abolished in 1985 but revived again in 2006.
The (appointed) New Zealand Legislative Council was abolished in 1951.
Nebraska is the only state in the United States to have a unicameral legislature, which it achieved when it abolished its lower house instead of the upper house in 1934. During the governorship of Jesse Ventura in Minnesota, he called for the state to have a unicameral legislature.
Bahia, Ceará, Pernambuco, São Paulo (1930), Croatia (2001), Denmark (1953), Egypt (2013), Greece (1935), Hungary, South Korea (1960), Peru (1992), Portugal (1926), Sweden (1970), Turkey (1980), Venezuela (1999) and Mauritania (2017) once possessed upper houses but abolished them to adopt unicameral systems.
In October 2013, a constitutional referendum in the Republic of Ireland proposed the establishment a unicameral system by abolishing Seanad Éireann, the upper house of parliament. The proposal was narrowly rejected by a margin of 51.7% against vs. 48.3% in favour.