This research aims to explore the ancient history of Korea through epidemics, specifically as recorded in Samguk-saki (三國史記). Since 2002, I have conducted a good deal of research concerning the epidemics and pandemics which occurred in Korea and other parts of East Asia during the time of the Three Kingdoms and Unified Silla. My research has brought to light several new pieces of information that historians have thus far overlooked Korea’s ancient history. First, I submit that many epidemics which occurred in ancient Korea broke out largely as a result of mass immigration and war. Second, in the 4th century, the new religion of Goguryeo, Buddhism, derived from the Northern and the Southern dynasties (南北朝) of China, brought new epidemics as well, which resulted in the Goguryeo people accepting Buddhism more rapidly. The same scenario played out in Japan, where the Buddhism was introduced by Baekje in the 6th century. Third, most of the pandemics in ancient Korea originated in China, and they sometimes spread from Korea to Japan. Fourth, some epidemics had political impact, as when an epidemic would take the life of a high-ranking or important figure, such as a king or political leader. For example, King Sunduck (宣德王:rg.780-785) died as the result of an epidemic, presumably smallpox. It was not only the king. Many aristocrats and members of the court were also killed at that time. There is no record of it, but that doesn’t mean it never happened. In ancient times, many people thought that epidemics were a punishment of Gods. Punishment from heaven would imply fault on the part of political leaders, who would in turn not want to record their shortcomings. As a result, Kim Kyungshin, King Wonsung (元聖王:rg.785-798), ascended the throne, even though another successor, Kim Jouwon(金周元), had already been chosen by the people of the court, including Qeen Jungui (貞懿太后), the daughter of King Sungduck (聖德王:rg.702-737) and the mother of King Sunduck. It appears that Kim Jouwon had fled from the smallpox, which was widespread in the court in 785. Kim Kyung-shin, however, was presumably more brave, waiting in the palace to inherit the throne as soon as King Sunduck died.prohibitio