The United Socialist Party (Partito Socialista Unitario, PSU) was a social-democratic political party in Italy, active from 1922 to 1930.
The party was founded in November 1922 by the reformist wing of the Italian Socialist Party (PSI) led by Filippo Turati and Giacomo Matteotti, after they had been expelled in October. A staunch opponent of Benito Mussolini and Fascism, Matteotti was assassinated by Fascist thugs, affiliated to Ceka, in June 1924. The event provoked the Aventine Secession). Outlawed in November 1925, the PSU became active in clandestinity, as the Italian Workers' Socialist Party (Partito Socialista dei Lavoratori Italiani, PSLI). In June 1930 the PSLI re-joined the PSI.
Leading members and activists of the party included Oddino Morgari, Sandro Pertini, Camillo Prampolini, Claudio Treves and Anna Kulischov.
The party was a member of the Labour and Socialist International between 1923 and 1930.[1]