Fifteenth century was the most brilliant period in the history of Korean science. Especially remarkable were the creative scientific and technological achievements made during the reigns of T'aejong and Sejong in the first half of the century: the rise of astronomy, calendrical science and agricultural meteorology, the growth of technology, the development of geography, and the establishment of Korean medico-pharmacology. Although a great deal more work needs to be done on many subjects, the results obtained so far have been sufficient to support the view that the Korean achievements during this period surpass——both in quality and in quantity——scientific and technological achievements of any other country of the same period. Yet, fifteenth century Korean science and technology has not been valued properly in the history of science of the world. This paper tries to correct this situation by reexamining the achievments of Korean science and technology in this period. The paper argues that with these achievements, which fill the gap between the Islamic science and the European modern science, the fifteenth-century should be viewed as the period of Korea in the world history of science.