Kaykaus II or Kayka'us II (Persian: عز الدين كيكاوس بن كيخسرو, ʿIzz ad-Dīn Kaykāwūs bin Kaykhusraw) was the eldest of three sons of Kaykhusraw II. He was a youth at the time of his father’s death in 1246 and could do little to prevent the Mongol conquest of Anatolia. For most of his tenure as the Seljuq Sultan of Rûm, he shared the throne with one or both of his brothers, Kilij Arslan IV and Kayqubad II. His mother was the daughter of a Greek priest, and it was the Greeks of Nicaea from whom he consistently sought aid throughout his life. Baiju threatened him and warned him of giving his Mongol cavalries new pastures in Anatolia and too late to pay tax. The Mongols defeated him and he,who defied Baiju, fled to the Byzantine Balkan in 1256. The Byzantine court detained him, though, they welcomed him as usual. So Kaykaus' brother Kayqubad appealed to Berke Khan of the Golden Horde. Nogai invaded the Empire in 1265 and released him and his men after Michael detained an envoy from Cairo to Berke. Berke gave Kaykaus appanage in Crimea and had him married the Mongol woman. He died an exile in 1279 or 1280 in the Crimea.
Though deposed and exiled, Kaykaus remained popular among the Turkmen of Anatolia and a threat to the stability of the fragile Seljuq-Mongol relationship. The vizier Fakhr al-Din Ali was imprisoned for a time in 1271 for corresponding with him. It was from Kaykaus that Karamanoğlu Mehmed Bey in 1276 sought help in his uprising against the Mongols. Since Kaykaus was in no position to help, Mehmed Bey thought it best to have a representative of Kaykaus’ line on his side, even if only an imposter, and named Jimri as head of the revolt. Kaykaus later dispatched several of his sons from the Crimea as pretenders, one of which, Masud II, was ultimately successful in winning the Seljuq throne in 1280.
In the Ottoman period the rebel Sheikh Bedreddin, who drew support largely from Turkmen migrants to the Balkans, claimed descent from Kaykaus II.