This paper examines the positions and personnel of the Naeui system in the late Joseon Dynasty. First, the regulations of the Naeui system were investigated through the literature related to Naeuiwon. Next, the operation of the regulations, changes in the system, and causes were analyzed through the Seungjeongwon Diary (承政院日記). We discovered: 1) Naeuiwon's medical bureaucracy originally did not have a fixed number of positions, but gradually came into being with a quota regulation. Uiyagdongcham-ui (議藥同參醫) and Naechim-ui (內鍼醫) did not have a quota, but was initially set at 10 people, then expanded to 12 people. Originally, the royal physician had no fixed number, and in 1864 the first quota was 7 people. 2) 'Gyeom-eoui' and 'gachanaeui' served to expand Naeui's quota. After the mid-17th century, 'Gyeom-eoui' expanded the quota of royal physicians to secure a position for the medical bureaucracy of Naeuiwon. 'Gachanae' after King Jeongjo serves to add to the quota while obeying the provisions of the law. 3) The customary promotion of Naeuiwon's medical bureaucracy expanded and became stricter after the mid-19th century, during which special promotions became more frequent than in previous periods. As for the provision of appointment to the 6th class after 30 months, Uiyagdongcham-ui was established in 1686 and Naechim-ui was established in 1718, increasing the chance for customary promotion. In the case of Naeui, the regulation for the Secretary General to raise the degree of official rank has been strengthened since the Cheoljong era. However, special promotions were frequent in the mid-19th century because the number of high-ranking officers increased compared to the previous period. In conclusion, the Naeui system in the late Joseon Dynasty changed in the direction of strengthening their own privileges. The Naeuiwon's quota was increased and promotion was guaranteed through the system and customs. Since the mid-18th century, there have been some regulatory restrictions, but the framework has not changed. This is confirmed not only in the regulations of the documents related to the Naeuiwon, but also in the Seungjeongwon Diary. Naeuiwon's medical bureaucracy enjoyed superiority in promotion and status compared to other forms of technical bureaucracy.