Güyük (c. 1206–1248) (also transliterated Guyuk, Kuyuk, Güyük, etc.) was the third Mongol khan, son of Ögedei Khan, grandson of Genghis Khan, who reigned from 1246 to 1248.

He served as a military officer, as did the other senior princes of the Mongol Empire, under Genghis and, mainly, Ögedei. In 1233, he conquered Puxian Wannu's Dongxia Kingdom.

He participated in the invasion of Russia and Europe in 1236-1241 with many of the other Mongol princes, including Batu. During the course of the invasion, however, Güyük quarreled violently with Batu, and was for a time recalled to Mongolia. This breach between the families of Jöchi and Ogedei would widen over time, and ultimately prove the downfall of the Mongol Empire.

In the meanwhile, however, Ögedei had died, his widow Töregene had taken over as regent, was in a position of great influence and authority, and used both to advocate for her son Güyük. In spite of Batu's withdrawal from Europe so that he might have some influence over the succession, and in spite of his dealying tactics, Töregene succeeded in getting Güyük proclaimed grand khan in 1246. Just after his succession, he received the mission of John of Plano Carpini.

He reversed several of the unpopular edicts of his mother the regent, and, though somewhat libertine, made a surprisingly capable khan, appointing Eljigidei in Persia (with designs for an attack on Baghdad) and pursuing the war against the Song Dynasty. Nevertheless, he was somewhat unpopular and insecure, executing several formerly high-ranking officials on grounds of treason. In 1248, he demanded Batu come towards Mongolia to meet him, a move that at least some at the time regarded as a pretext for Batu's arrest.

However, this showdown never came to be—Güyük died on the way at about forty-two of the combined effects of alcoholism and gout. His widow Oghul Ghaimish took over as regent, but she would be unable to keep the succession within her branch of the family, as Möngke succeeded as khan in 1251.

The reign of Güyük, then, showed that the family split between Batu's line, the descendants of Jöchi, and the rest of the family might well be the fatal flaw for the unity of all the khanates, and civil war might well have occurred, had he not died early.