The Sidna 'Ali Mosque (Arabic: مسجد سيدنا علي, Masjid Sidna 'Ali; Hebrew: מסגד סידנא עלי, Misgad Sidna Ali) is a mosque located in the depopulated village of Al-Haram on the beach in the northern part of Herzliya in Israel. It serves as both a mosque and a religious school.
The mosque is situated around a tomb reputed to be that of a local saint, Ali b. Alim who died in 1081. Ali was described as great scholar and miracle worker by Baybars' biographer, Muhyi al-Din (died 1292). According to Mujir al-Din (writing c. 1496), the mosque was visited by Baybars in 1265. Baybars prayed for victory before retaking Arsuf from the crusaders. An annual festival that was attested here in the 15th century continued up to the 1940s.
The existing building contains parts of differing ages of construction and repair, though none from before the 15th century. The part of the building described as the oldest in 1950 has since disappeared. The minaret was destroyed by naval bombardment in World War I and since rebuilt. Major repair work was done in 1926, the 1950s and 1991–1992.