The Unitary Socialist Party (Partito Socialista Unitario, PSU) was a democratic socialist political party in Italy active from 1922 to 1930. Its outlook was reformist and anti-fascist.
Outlawed in November 1925, the PSU remained active as the clandestine 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.[4]