China’s borderlands provided a fertile ground for Protestant missions and Chinese churches to win converts outside the Han-dominated region. This proselytizing agenda took on a new political meaning during the Anti-Japanese War (1937–1945), when the Nationalist Party became concerned about the security of Chinese frontiers. After relocating to the wartime capital of Chongqing in November 1937, the Nationalists recognized the Southwest border regions as key to national revival and found it necessary to control the frontier populations and resources. This chapter reconstructs the history of the Border Service Department, a joint venture founded by the Chinese Church of Christ and the Nationalist state in December 1939 to undertake medical and educational work in the Sichuan-Tibet-Xikang border areas. Funded by wartime Nationalist officials and supervised by Chinese church leaders, the Border Service Department built a solid anti-Japanese rear-defense area in China’s Southwest, improving peoples’ livelihood and integrating these border regions into the Republican administration.