Abu Al-Hasan 'Ali ibn 'Othman (c. 1297 - May 24, 1351) (Arabic: أبو الحسن علي بن عثمان‎) was a sultan of the Marinid Dynasty who reigned in Morocco and Al-Andalus (r. 1331 - 1351).

He succeeded his father Abu Sa'id Uthman II. He won a great naval victory in Iberia at Gibraltar (April 5, 1340). In the same year he was however defeated by land against the united forces of Alfonso XI of Castile and Afonso IV of Portugal in the battle of Rio Salado. After this defeat, Al-Hasan was forced to end warfare and conquest in the Iberian Peninsula.

In Algeria, Al-Hasan captured in 1337, after a three-year siege, the town of Tlemcen. He married the daughter of Abu Sa'id, member of Hafsid dynasty. After Abu Sa'id's deaths, Al-Hasan invaded Tunisia. He captured Tunis in 1347, but was heavily defeated in battle next year by the united Arab tribes of Tunisia, and forced to abandon Tunisia.

Al-Hasan abdicated in 1351 in favour of his son Abu Inan.