Al-Mahdi Ali bin Mohammed (September 25, 1305 - 1372) was an imam of the Zaidi state in Yemen who ruled in 1349–1372.
Ali bin Muhammad al-Hosni was born in the village al-Ahani in the Sa'dah area in northern Yemen.
In 1346, the learned and powerful Imam al-Mu'ayyad Yahya died, and no politically strong figure emerged in his stead.
In the presence of a numerous congregation of Zaidi scholars, he adopted the title al-Mahdi Ali and took possession of Sa'dah and Dhamar.
The Rasulid emir of Hadar, Nur ad-Din Muhammad bin Mika'il, turned rebellious against Sultan al-Mujahid Ali in 1359.