The Al-Omari Grand Mosque (Arabic: المسجد العمري الكبير), known as Jami' Al-Kabir, is a Sunni Islam mosque, located in the central district of Beirut, in Lebanon.

The building has been a place of worship including its original use as a Roman temple, and subsequently as a Roman church, before Beirut was conquered by Mamluk Egypt and it was converted into a mosque.

The Al-Omari Grand Mosque was originally a Roman temple, dedicated to the god Jupiter. The Ancient Roman influence is visible in some of the architectural elements, including the building's columns and foundations.

During the Byzantine era, the building was made into a Roman basilica that featured intricate mosaics and architectural elements of the Byzantine style. In the 7th century CE, the basilica was converted into a mosque. During the Crusader occupation of Beirut, in the 12th century, the mosque was converted into the Church of Saint John. Similar Romanesque churches with triple apses were built in Tyre and Tartus, using recuperated material such as Roman columns and capitals.

In 1291, in the Ottoman era, the Mamluks captured Beirut, and under Islamic conquest the church was again converted into a mosque. It was renamed Al-Omari Mosque after the second caliph, and became known as "Jami' Al-Kabir", or the Great Mosque. Its Mamluk-style entrance and domes and minarets were added in 1350, reflecting traces of the former church's Byzantine style.

Badly damaged during the Lebanese Civil War, the mosque's refurbishment was completed in 2004, under the direction of Youssef Haidar.

• Islam in Lebanon
• List of mosques in Lebanon

Media related to Al-Omari Grand Mosque at Wikimedia Commons