Jeong Seon(a.k.a. Gyeomjae, 1676-1759) is now generally regarded as a master artist of late Joseon who made distinguished achievements and played a key role in the development of various painting genres such as jingyeong (true-view) landscapes, ideal landscapes, poetry-inspired painting, Southern School painting and historical figure painting. He maintained close relationships with leading figures in both Old Doctrine(Noron) and Young Doctrine(Soron), the two most influential political factions of late Joseon. This study is focused on some of the western painting techniques used by Jeong Seon,, and it concludes that he was one of the most innovative artists, one who brought new trends and techniques to the Korean art of the 18th century. Jeong Seon started his career as a government official by serving as an astronomy instructor in the Office of Astronomy and Geomancy( Gwansanggam ), a government agency responsible for affairs relating to the knowledge of astronomy, natural science and mathematics developed in the western world. The Joseon Dynasty of the 18 th century regarded astronomy as particularly important, assigning instructors like Jeong Seon to the education and assessment of the public functionaries working in Gwansanggam, and appraising their teaching capabilities through regular tests. It is highly probable that Jeong Seon himself participated in the production of paintings, illustrations, maps and astronomical charts required for the programs of compiling, copying and publishing books on astronomy. Jeong Seon is known to have set up friendly relations with the leaders of the Old Doctrine(Noron) who were critical of Western Learning( Seohak), while also maintaining a close relationship with the Young Doctrine(Soron) who were supportive of that learning and insisted that the scientific and technological achievements made in the West should be adopted. It was his close relationships with the Soron that guided Jeong Seon to Western Learning and to western paintings. In this study, the techniques of western art Jeong Seon adopted are discussed according to four criteria. While these criteria are all related to the techniques of western art, the Discussion starts with detailed elements such as the representations of the land surface and atmospheric effect, and proceeds to elements more essential, but more deeply fused with tradition, such as perspective. This approach is deemed appropriate considering that the techniques of western origin are integrated with the traditional so successfully in his works that it is not easy to discern the influences that came from western art. Paintings by Jeong Seon show that the artist began to use western techniques when he was in his thirties, and continued to use them up to his final years. The techniques were first used in his jingyeong paintings depicting real landscapes as they were viewed by the artist, and were gradually extended to his other works, eventually establishing the features that were characteristic of his art. His use of western techniques is regarded as significant in that it is one of the earliest case showing the influence of western art on the landscape paintings of Joseon, and also in that it suggests he was an intellectual with a keen interest in progressive ideas and culture. His true-view paintings should be regarded as evidence of his reluctance to accept the framework of the traditional world view based on Sinocentrism. Jeong Seon, in conclusion, was an intellectual who sought after change and innovation in the face of the changes occurring in the ideologies, politics and culture of 18th century Joseon, and an artist of a new kind who created new value and meaning in his paintings.