After the Mongol invasion of Tibet in 1240, the abbot of the Sakyapa (Sa-skya-pa) sect was dispatched to show submission to the Mongols. After that, this sect ruled Tibet with the support of the Great Khans until the end of the Empire even though there were ups and downs. From then on, this political system which was established by connecting with outside force, namely Patron and Priest Relationship (Tib. yon-cho, yon-mchod), formed the basis of the Tibetan politics. In this sense, the Mongol Empire period has significance in Tibetan history. However, while there are lots of studies on the Persian or Chinese records of the Mongol invasion, there have been practically no researches on the Tibetan perceptions of the Mongols. It was the first time that Tibet was invaded by ‘alien’ power since the Tibetan Empire period (618-842) so it would have been a shock to the Tibetan people, too. Therefore, it would be worth examining what the Tibetan people thought of the Mongol invaders during the Mongol Empire period. This thesis suggests several points about the Tibetan perceptions of the Mongols. Firstly, on the 'invasion', non-Sakyapa records tell that high monks of their sects repelled the Mongol enemy with the power of Buddhism, stone rain for example. On the other hand, Sakyapa records emphasized that the Mongols were brutal and stupid, which the Sakya leaders could not just ignore. So the leaders should go and submit to the Mongols in order to educate the barbarians with Buddhism. In short, the monks who were summoned to Mongol court said that it was for the spread of Buddhism, especially Tibetan Buddhism against Christianity and Chinese Buddhism. What is noticeable next is that the Tibetans blamed Tibetan people who visited the Mongols and got the power, rather than the Mongols. Many records that repeatedly mentioned the inevitability of visiting and serving the Mongols are the counterevidence that there were criticisms of those monks. While non-Sakyapa sources didn't criticize famous Phagpa('Phags-pa), the Sakyapa's writing records that he was criticized severely. Thirdly, we can see that Tibetan people complained the heavy tax and corvee imposed by the Mongols. Especially the compulsory post service ('u lag) was said to be the heaviest burden for them. For example, most of the households of some myriarchies were postal-households (站戶) to sustain the post stations, which is one of the main features of Tibetan situation during the Mongol period. Lastly, the Sakyapa sect firstly opened the door to a new political system, yon-cho (yon-mchod), which provoked criticism among contemporary Tibetan people. But in the long run, it became the feature of Tibetan politics. About two hundred years later, the newly-risen Gelukpa (Dge-lugs-pa) sect, did not have to counter-argue about her relations with the Altan Khan of the Mongol Tumeds like the predecessor, the Sakyapa.