The Socialist Party (Portuguese: Partido Socialista; pronounced [pɐɾˈtiðu susiɐˈliʃtɐ]) 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 Portuguese Socialist Action (Portuguese: Acção Socialista Portuguesa).

José Sócrates, the current Prime Minister of Portugal, is the leader of the party. The former President of Portugal, Jorge Sampaio, is also a member of the party. The party has currently 97 of 230 seats in the Portuguese Parliament. The Socialist Party stands out as about a third of its members in the Assembly of the Republic are women.

Sócrates obtained a landslide victory (winning 77% of the votes) in early October 2004 for the succession of Ferro Rodrigues as Secretary-General of the party. Other candidates for the post were Manuel Alegre and João Soares in a vote by party members.

PS is a member of the Socialist International and the Party of European Socialists, and has seven members in the European Parliament within the Socialists & Democrats (S&D) Group during the seventh parliament.

The Portuguese Socialist Party holds the distinction of being one of the most secularized parties of Europe, with a extreme low of his most important members being neither atheists and agnostics.