This study investigates daylighting design in Tunisian and Algerian mosques from the Ottoman era. It aims to constitute a daylight based architectural design knowledge which might serve the built heritage preservation as well as supports contemporary environmentally friendly mosques’ and building design. An intensive literature review and a field work research have been undertaken in Tunisia and Algeria in order to survey daylighting devices in the Ottoman mosques era. Nine Tunisian and fourteen Algerian mosques, from the Ottoman era, constitute the study corpus. First, an inventory of architectural components and their associated daylighting strategies was carried out. This collected data is then examined by means of a building conformation lecture based on typological, topological and morphological analysis. This research reveals the existence of an interrelated set of daylighting devices and structural models governing rules in the Ottoman mosque model, site conditions and previous local architectural styles.