The Yemeni Socialist Party (Arabic: الحزب الاشتراكي اليمني, al-Hizb al-Ishtiraki al-Yamani, YSP), officially the Socialist Party Organization (Arabic: منظمة الحزب الاشتراكي), is a social democratic political party in Yemen. A successor of Yemen’s National Liberation Front, it was the ruling party in South Yemen until Yemeni unification in 1990. Originally Marxist–Leninist, the party has gradually evolved into a social democratic opposition party in today’s unified Yemen.

Following the outbreak of the Yemeni Civil War, the party split into two factions; one remained in Yemen and labelled itself the “YSP – Anti-Aggression” and declared its loyalty to the Houthis and their leader Abd al-Malik al-Houthi, while much of the party’s leadership, including Abdulrahman al-Saqqaf and Yasin Said Numan, went into exile in Riyadh and backed the government of Abdrabbuh Mansour Hadi. After the split, the “Anti-Aggression” faction issued statements that they consider the leadership in Riyadh to have been expelled from the party for of their support of the Saudi-led intervention in Yemen, calling for their punishment as a result.

The “Anti-Aggression” faction declared its opposition to the Saudi-led coalition, vowing to aid the Houthis in defeating it. Notably, this faction of the YSP actively helped facilitate the Houthi entry into Ta’izz during the battle for the city, one of the YSP’s historic centers. In 2016, it denounced the United Nations for removing Saudi Arabia from the list of countries responsible for harming children. They also condemned the Trump administration’s decision to designate the Houthis as a terrorist group.