The Omar Ali Saifuddien Mosque (Malay: Masjid Omar Ali Saifuddien) or unofficially Sultan Omar Ali Saifuddin Mosque (SOAS Mosque), is a mosque in Bandar Seri Begawan, the capital of Brunei. Omar Ali Saifuddien III, the 28th Sultan of Brunei, is credited with building the mosque, thus its name. It is one of the two state mosques (masjid negara), the other Jame' Asr Hassanil Bolkiah Mosque. One of the biggest and most striking mosques in the Far East, it was completed in 1958 at a cost of $5 million USD. The Mughal architecture of India had a significant effect on the design.

The mosque is recognisable by its gold dome that dominates the city's skyline. It is situated in the middle of a man-made lagoon with a ceremonial stone barge. The inside is decorated with rugs from Saudi Arabia and walls made of Italian marble. The mosque is a popular tourist destination due to its façade, but its main purpose is to be a place of worship. It has since become the most photographed icon in the country.