The Socialist Party (Portuguese: Partido Socialista, pronounced [pɐɾˈtiðu susiɐˈliʃtɐ], PS) is a social-democratic political party in Portugal. It was founded on 19 April 1973 in the German city of Bad Münstereifel by militants from the Portuguese Socialist Action (Portuguese: Acção Socialista Portuguesa). The PS is a member of the Socialist International, Progressive Alliance and Party of European Socialists, and has nine members in the European Parliament within the Progressive Alliance of Socialists and Democrats group during the 9th European Parliament.

A party of the centre-left, the PS is one of the two major parties in Portuguese politics, its rival being the Social Democratic Party (PSD) on the centre-right. The leader of the PS is António Costa, the current Prime Minister of Portugal. The party won 120 of 230 seats in the Portuguese parliament following the January 2022 election, enough to form a majority government.