The nineteenth century was marked by a rapid and widespread expansion of foreign missionary activities among all the Churches in the USA and Europe. In addition to sending missionaries all over the world to preach the Bible, both American and European missionary organizations also aimed to bring “true” Christianity to the peoples of the Ottoman Empire. While seeking converts to the Christianity it soon became clear that there was little point in attempting to proselytize among the Muslims because missionary activities among them were illegal in the region. Therefore, the Western missionaries concentrated primarily on the Christian minorities in the Middle East, including Armenians, Greeks, Jacobites, Nestorians, Chaldeans, Copts, and Maronites. The purpose of the paper is to present a history of the American missionary activities in Mardin in the nineteenth century. I will be particularly interested in the activities of the American Board of Commissioners for Foreign Missions (ABCFM) which was the most substantial American missionary organization in the Ottoman Empire throughout the nineteenth century. The ABCFM sent its missionaries to the Middle East in 1820 and several exploratory journeys were undertaken during the early decades of the ABCFM mainly to investigate conditions in the region, to find suitable locations for mission stations and congregations to be evangelized. Mardin was one of the suitable places that the ABCFM decided to open a mission station. In addition to educational and medical work (operating hospital), the missionaries in Mardin distributed copies of the Bible and other religious tracts in the vernacular, in order to reach those to whom they referred as the “nominal Christians” of the Eastern Churches. In my paper, I will present a brief history of the ABCFM missionary activities and schools in Mardin and explain the characteristics of these activities in the period that began with the arrival of the first group of missionaries at Mardin until the beginning of the 20th century. Moreover, I investigate the impact of these activities on the peoples of Mardin and the reaction of the Ottoman authorities. Last, examining the efforts of the American missionaries to seek converts among the minorities in the Empire to the Protestant faith helps us understanding the religious, moral, intellectual and social situation in the region. I use primary sources such as letters, diaries, annual reports, journals, school records, pamphlets, and newspapers of the missionaries as well as the secondary sources and pictorial materials.