Four of the Koryǒ dynasty's earliest kiln sites are studied for the macroscopic, compositional, and microstructural characteristics of their celadon products. Recent excavation of Sǒri and surface investigation of Kangjin sites provided new materials for closer examination of the origin and early developments of celadon technology in traditional Korea. Two other sites, Wǒnhǔngni and Osari, with archaeological characteristics in common with the oldest layer of Sǒri, are also examined. Principal component analysis of body composition shows thai Sǒri and Kangjin had better control in their choice of raw materials whereas Wǒnhǔngnt and Osari had much wider scatter, showing the more experimental nature of their operation. The early Kangjin grouped out separately primarily because of their higher Al2O3 content, while X‐ray diffraction patterns indicate they might have been fired at a higher temperature than other groups. The Korean method of two‐step firing, first at a lower temperature to bake imglazed bodies and then at a higher temperature after glazing, is evident from the earliest operations in Kangjin.