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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) was a social-democratic political party in Italy existing from 1949 to 1951.

The party was founded by some moderate members of the Italian Socialist Party, which had unsuccessfully asked to stop the collaboration of their former party with the Italian Communist Party, and some leftist members of the Italian Socialist Workers' Party which unsuccessfully asked for a rupture with the Italian Christian Democracy and the 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 the Italian Socialist to overrun both the Communists and the Christian Democrats. The project had strong international supports through the Socialist International: the SFIO and the British Labour, at time supporting the Georges Bidault’s government and ruling the Attlee ministry, liked the idea of their Italian sister counterpart defeating both USSR and United States funded leading parties, mirroring the interests of France and the UK. However, under all aspects the project was definitely too ambitious.

On 1 May 1951, the party fused with the Italian Socialist Workers' Party, previously founded by the reformist wing of the Italian Socialist Party in 1947 and led by Giuseppe Saragat, to give birth to the Italian Democratic Socialist Party (PSDI).