The Ankara Agreement (1921) was signed on 20 October 1921 at Ankara between France and the Grand National Assembly of Turkey, ending the Franco-Turkish War. Based on the terms of the agreement, the French acknowledged the end of the Franco-Turkish War and ceded large areas to Turkey. In return, the Turkish government acknowledged French imperial sovereignty over the French Mandate of Syria. The treaty was registered in League of Nations Treaty Series on 30 August 1926.

This treaty changed the Syria–Turkey border set by the 1920 Treaty of Sèvres to the benefit of Turkey, ceding it large areas of the Aleppo and Adana vilayets. From west to east, the cities and districts of Adana, Osmaniye, Marash, Aintab, Kilis, Urfa, Mardin, Nusaybin, and Jazirat ibn Umar (Cizre) were consequently ceded to Turkey. The border was to run from the Mediterranean Sea immediately south of Payas to Meidan Ekbis (which would remain in Syria), then bend towards the south-east, running between Marsova (Mersawa) in the Sharran district of Syria and Karnaba and Kilis in Turkey, to join the Baghdad Railway at Al-Rai From there it would follow the railway track to Nusaybin, with the border being on the Syrian side of the track, leaving the track in Turkish territory. From Nusaybin it would follow the old road to Jazirat ibn Umar, with the road being in Turkish territory, although both countries could use it.