This mosque, located on the west side of Place Mohammed Khemisti was built in 1296/696 AH and is named in honor of Abu El Hassan Ben Yekhlef Ettenessi, a celebrated jurist and scholar. During the French colonial period is was appropriated and served multiple purposes, including a storiage facility for animal feed, a school, and a museum. According to Discover Islamic Art,

Over the last few years, the museum has been transferred into part of the old madrasa in Tlemcen's 20th August Street, and the building has been restored.

The prayer room is accessed by three doors and features onyx columns. Arcades of horseshoe arches create three naves perpendicular to the walls of the quibla. Some of the original decoration in the interior has been preserved, especially along the north side.

The ceiling is carved cedar wood, and according to the website Vitaminedz was restored by the Fardheb from Tlemcen. The horseshoe arch mihrab is decorated with carved plaster in floral and calligraphic motifs. It is covered by a dome muqarnas. The brick minaret is in the southeast corner of the building. The upper platform is accessed by a circular staircase in the interior.

The exterior of all four sides of the minaret are decorated with rectangular panels divided into a diamond grid. The entrances are all decorated, cusped, horseshoe arches, carved plaster, and zellij. The roof is covered in the green tile characteristic of mosques in the region.

Sources:

Lafer, Ali. "Discover Islamic Art – Virtual Museum." Djama’a Sidi Bel-Hasan (mosque). Trans. Maria Vlotides. Discover Islamic Art – Virtual Museum, n.d. Web. 10 Sept. 2014. http://www.discoverislamicart.org/database_item.php?id=monument;ISL;dz;Mon01;5;en.

"Mosquée De Sidi Bel Hasan." Qantara. N.p., n.d. Web. 10 Sept. 2014. http://www.qantara-med.org/qantara4/public/show_document.php?do_id=742

"MOSQUEE DE SIDI BEL HASSAN." Vitaminedz.com. N.p., n.d. Web. 10 Sept. 2014. http://www.vitaminedz.com/mosquee-de-sidi-bel-hassan/Articles_673_240326_13_1.html.