Youssef Dey Mosque, or Sidi Youssef Mosque, is a historic Ottoman-era mosque located in the old city of Tunis in Tunisia. The mosque was founded as a small mosque in the year 1612 AD by Yusuf Dey (Youssef Dey,) the Dey of Tunis during the Ottoman era, who then opened it as an Friday mosque in the year 1631. The mosque, which includes the mausoleum of Youssef Dey, was restored in the 19th century and then inscribed as a UNESCO World Heritage Site in 1979 as part of Medina of Tunis.

The mosque named after its founder is of special interest because. while introducing new elements to the architectural plan and program, it preserves many aspects of the Ifriqiyan mosque. The prayer hall is no longer preceded by a courtyard, but framed by courses to the east, north and west. Along the northern façade, the portico plays the role of tribune-narthex of the local mosques. on the northwest corner stands an octagonal minaret, above a square base. It ends with a balcony protected by a wooden canopy, the ensemble is crowned by a lantern with a pyramid roof covered with green tiles. This octagonal tower will serve as a model for the Hammouda Pasha Mosque, the Al-Jedid Mosque and the Youssef Sahib El-Tabaa Mosque.