Sam-guk-sa-ki(三國史記) and Sam-guk-you-sa(三國遺事) is very important to systemize the Korean ancient history. Sam-guk-you-sa contain a more native religion or traditional culture. Because the material for Korean ancient history recorded at after middle era of Corea(高麗), it include many fairy ideal contents in the process of transmit for 500 or 1000 years. Especially, Sam-guk-you-sa recorded the fairy religions and affair mainly. Naturally, the major part of Sam-guk-you-sa is folktales which consisted a fairy story. The contents of every chapter of Sam-guk-you-sa filled with folktales, and among them, there is describe 2 over folktales. Though the fairy story describe simply in one or two sentence, in origin, it was substantial folktales. When this story recorded, the part which did not need in that society erased and remain a skeleton of the story. As this. the whole part of Sam-guk-you-sa states on the base of folktales. Folktales which recorded in Sam-guk-you-sa shows the main stream of historical progress of Korean ancient history. Especially, many folktales in chapter ‘Gi-Yi’(奇異篇) let we establish the system of Korean ancient history and many other buddhist karma tales help us to systemize Korean ancient buddhism history. From the folktale which recorded in Sam-guk-you-sa, we can reveal the Korean ancient social status. If we review the change of states about symbolic person or event carefully, we can find the group which got hegemony and manage that society and their disappearance. In many case, the folktales tell us historical truth. Though it does not transmit the each fact exactly, but it maintain the truth through improved parts by recorder omitted in the process of transmit. Not only Folktales which recorded in Sam-guk-you-sa let we know about native religions and crudely social phenomenon in Korean ancient, it add the newly religion and idea during transmit. In that case, true phenomenon of ancient society can distort. This aspect of folktales materials remain a limitation for reconstruct the ancient society. By compare with Official history and material for chronology, if we analyze the material for history which transmit as folktales positively, the true phenomenon of ancient society can reconstruct exactly.