Mansur ibn Nasir (d.1104) was the sixth ruler of the Hammadids in Algeria (1088-1104).

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Under al-Mansur, the son of Nasir ibn Alnas (1062-1088) the decline of the Hammadid kingdom began. Although he managed to conquer Algeria from the Almoravids with Bedouin assistance, he was unable to keep the unruly Bedouin tribes under control. The long-term security of roads and trade routes was no longer possible, to the increasing detriment of trade and agriculture - part of the harvest had to be given up to the Bedouin.

The lack of security inland led to an increase in the importance of sea trade, making the Mediterranean port of Bejaia the most important economic centre in the kingdom at the expense of the old capital Qalaat Beni Hammad. There was a steady migration of people from Al-Qa'la to Bejaia. To contemporaries, the luxury of the Hammadids and the spiritual life of the kingdom were at their most evident in Bejaia.

Under Mansur's son Aziz ibn Mansur (1104-1121) the capital was finally moved to Bejaia and Al-Qa'la was abandoned.