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Unitary Socialist Party
Partito Socialista Unitario
LeaderGiuseppe Romita
FoundedDecember 7, 1949 (1949-12-07)
DissolvedMay 1, 1951 (1951-05-01)
Merger ofRight-wing of the PSI
Part of Union of Socialists
Left-wing of the PSLI
Merged intoSocialist Party (Italian Section of the Socialist International)
IdeologySocial democracy
Political positionLeft
International affiliationSocialist International
Colours  Red

The Unitary Socialist Party (Italian: Partito Socialista Unitario; PSU) was a social-democratic political party in Italy that existed from 1949 to 1951.

The party was founded by moderate members of the Italian Socialist Party, who had unsuccessfully tried to stop the collaboration of their former party with the Italian Communist Party, and some leftist members of the Italian Socialist Workers' Party (Partito Socialista dei Lavoratori Italiani; PSLI), who sought a rupture with Italian Christian Democracy and NATO. The party was led by a former Minister of Interior, Giuseppe Romita.

There were 15 MPs who joined the party.

The goal of the party, which considered itself as transitional, was to reunite all Italian Socialists in order to overrun both the Communists and the Christian Democrats. The project had strong international support through the Socialist International: the French SFIO and the British Labour Party, at that time both in government, liked the idea of their Italian counterpart defeating parties funded by the USSR and the United States respectively.

However, the project was undoubtedly too ambitious, and it quickly stalled. On 1 May 1951, the party fused with the PSLI, led by Giuseppe Saragat, to give birth to the Italian Democratic Socialist Party (Partito Socialista Democratico Italiano; PSDI).