In this paper the author discusses turγaγ, hostages sent to the Yuan court by the royal house of Koryo, as one of the institutions in political relationship between Koryo and Yuan. He focuses on the fact that turγaγ were members of kesig, the imperial bodyguards, and regards the kesig system appears the most significance in the turγaγ system. From 1271 until the middle of the fourteenth century, the royal house of Koryo continued to send turγaγ and make them participate in kesig. As a result, almost all the kings experienced kesig before their accession to the throne. The kesig system was important in unifyling the political ruling class that constitute the Mongol Empire, and organizing a foundation of imperial power. It worked as a hostage system restraining the political ruling class, and worked as a way to train these hostages to become members of the ruling class. A bodyguard's devotion was regarded as a merit to the emperor, and the status was regarded as an honorable privilege which received the emperor's faver. Such kesig functions and significance affected the royal house of Koryo, too, and the royal family took advantage of it. At that time, the kings of Koryo became imperial sons-in-law, and received high statusas feudal lords under the Yuan Empire. Participation in kesig was significant as motivation for such status.