Qal'at Ja'bar (Arabic: قلعة جعبر, Turkish: Caber Kalesi) is a castle on the left bank of Lake Assad in Raqqa Governorate, Syria.

In 1168, Qal'at Ja'bar passed into the hands of Zengi's son Nur ad-Din, who undertook major construction works at the castle.

[1][5][6] Suleyman Shah, the grandfather of Osman I (progenitor of the Ottoman Empire), reputedly drowned in the Euphrates near Qal'at Ja'bar, and was buried near the castle.

However, it is probable that this story resulted from a confusion between Suleyman Shah, and Sulayman bin Kutalmish, the founder of the Seljuk Sultanate of Rûm.

[7] In 1973, in response to the rising water level of the newly created Lake Assad, the reputed tomb of Suleyman Shah and the associated exclave were moved to a new location north of Qal'at Ja'bar and the castle itself became Syrian territory.

[10] Syrian Democratic Forces captured the site on 6 January 2017 as part of its Raqqa offensive, seizing it after killing 22 ISIL fighters.

In anticipation of the filling of the reservoir, excavations and restoration works were carried out at numerous sites in the region, including Qal'at Ja'bar.

Although the location of Qal'at Ja'bar on a prominent hilltop ensured that it would not be flooded, the eventual lake level would turn the castle into an island.

In addition, parts of the western ramparts were restored, as well as the donjon Alia, which was intended to house a museum for the finds of the excavations at the castle.