The article is devoted to the study of new manuscript materials from the collection of the Institute of Oriental Manuscripts of the Russian Academy of Sciences on the relations between members of the Korean diplomatic mission and the Russian Orthodox Mission in Beijing. The letters, written in the first 20 years of the 19th century, contain correspondence between the members of the two countries' missions, which cannot be found in contemporary historical sources. This article is devoted to studying the addressee of the members of the Korean diplomatic mission, putting all the letters in order, and clarifying their historical value in the study of Sino-Russian-Korean relations on the eve of the modern time. The novelty of the study lies in the fact that these manuscripts, closely related to the activities of the great Russian sinologist N. Ya. Bichurin, have not been studied before. According to the content of these letters, Bichurin communicated with the Koreans on the model of educated Chinese people, and one of the purposes of communication between the envoys of the two countries was the acquisition of different information. The relevance of the study is caused by the growing scientific interest of scholars in new manuscript materials about the history of Russian sinology and Russian-Korean relations.