Following the emergence of the first centers of Protestant Christianity in England (late eighteenth century AD), Advertising Association in Africa and East (1799 CE / 1214 AH) – which was later to be called the Church Missionary Society (1812 CE / 1227 AH) – came into existence. Despite its rather late emergence by comparison with the other Christian bodies active in the nineteenth-century Iran, this association turned out well and popular as one of the two major pillars of the Protestant Church until the Islamic Revolution of Iran. It owed this success not only to the domain of its propaganda in Iran within the political influence of the imperial Britain but also to the benefit it took from the experiences of other communities which prioritized educational and health services. In the meantime, the Association’s missionaries – who benefited from the political support of the state to which they belonged as well as Iran’s backwardness in terms of education and health – put a variety of ways and means to the test in order to gain social legitimacy. To discuss the workings of the Church Missionary Society in Qajar Era, particularly until the Constitutionalists’ Revolution of Iran, the present article aims to analyze not only the keys but also the barriers to the success of such an association. This research is carried out by means of the historical analysis method.