Al-Mansur al-Husayn (1669–1720) was an Imam over parts of Yemen, who ruled in rivalry with other competitors in 1716–1720.
He claimed the imamate in the strong fortification Shaharah in 1716, taking the name al-Mansur.
A large part of the country quickly fell away from the unpopular al-Mahdi Muhammad.
Al-Qasim soon defected from his uncle, acknowledged al-Mansur al-Husayn, and besieged the old imam.
He controlled San'a and the seaports, while al-Mansur al-Husayn merely held Shaharah and some surrounding territories.