Since Korea disclaimed to open the ports, Korean architecture has met the impetuous transformation. Although there would be various factors of this transformation, the new-coming architecture by missionary seemed to be a significant one, and many researches have been carried out on this theme in diverse viewpoints. However, because these researches have preponderated on the Catholic tradition, it is deficient for clarify the whole history of mission architecture. Therefore, this research has the meaning to enrich the history of Korean modern architecture by making balance. First of all, this paper is focused on the activities of one missionary, Graham Lee. He is a practical missionary at the beginning, his architecture made a critical influence in Korean traditional architecture. Graham Lee was born in Rock Island, Illinois, 1861, and he determined to become a missionary through grown up. He spent his boyhood by working as a plumber for his purpose and studied in a university afterward. Graduating of McComick Theological Seminary, he was nominated as a pioneer of Pyeng Yang Mission Station and set foot in Korea, September of 1892. Since then he started to erect missionary facilities in Pyeng Yang, such as Well House(1898), Pyeng Yang Central Church(1900-1901), Pyeng Yang Academy(1902). These all his works are designed with eclectic style which shows western and Korean traditional style intermingled. This unique characteristic made a profound influence to the Korean mission architecture afterwards. Especially, the L-type plan of Pyeng Yang Central Church, which is first shown by him, is recognized very unique, and this plan type had been spread all over the country. Therefore the L-type plan became the peculiar feature of the early Korean churches. Furthermore, working with Korean carpenters, he taught them new skills of modem buildings. After that, they were expanded out northern part of Korea and took the roles of master builders. According to this expansion, his particular style had got spread and had been settled as a unique eclectic style in Korean modern architecture. In the conclusion, he is evaluated to be a critical pioneer missionary, who left a big influence on the frame work of Korean modern architecture in the transitional times.