This mosque is located in the south of Qalat Bani Hammad, near its longitudinal center. The mosque is quite large, with a rectangular plan measuring 56 meters wide east-to-west and 64 meters long north-to-south. The longitudinal axis of the mosque aligns with the north-south meridian. A minaret is located at the center of the north wall, while public entrances in the east and west walls open into the mosque courtyard. Bordered by arcaded galleries, the large sahn leads to the hypostyle prayer hall, which is divided by columns into a grid thirteen aisles wide and eight bays deep. The mosque featured a large maqsura, now destroyed, occupying an area five bays wide and four bays deep in front of the qibla niche on the south wall. The Qalat Beni Hammad mosque would be one of the largest in all of Algeria, were it not mostly demolished today.
Unfortunately, almost all of the structures visible today at the Qalat Bani Hammad have survived only as unroofed foundations of demolished structures. The only structure to persist beyond vestiges of a plan at ground level is the minaret of the qalat's great mosque. The minaret is a masonry structure composed of stone bricks laid in a coursed ashlar pattern. The square plan of the minaret recalls Andalusian examples, while the arrangement of the arches on its exterior likely derives from Fatimid Egypt. The south elevation of the tower features a tripartite organization, in which lobed arched openings in the central third of the wall are flanked by decorative blind arches with taller and narrower proportions. Originally the semi-circular blind arches on the south elevation were lined with polychrome tiles, while the other faces of the minaret were left as blank masonry surfaces. A rectangular doorway is set into the arched opening at the ground level, providing access to a narrow winding interior stair that leads to the upper levels of the tower. A small rectangular stone panel bearing a carved inscription and vegetal patterning is inset above the entrance portal. The lower six levels of the minaret stand today, with arched openings on the south elevation at the third, fourth, and fifth levels. The top of the minaret deteriorates into rubble 25 meters above the ground, and any balcony or decorative rooftop structures have been destroyed.