The Indian peninsula is the region with the longest religious history in the world. Religion runs through the historical development process from ancient India to British India, and then to the partition between India and Pakistan. After the second world war, with the booming of national movement for emancipation, coupled with British India suffering from intensified confrontation between hindus and muslims, suzerain Britain introduced the ‘Mountbatten Plan’ to admit Muslim to establish a separated regime, which ultimately led to the construction of India nation-state in 1950, and the formation of Pakistan followed in 1956. Religious factors played an important role in the nation-state construction, as well as in various fields including politics, economy and so on after the establishment of the two countries. After a comparative analysis of the Hinduism’s role in the founding of India and that of Islam in the founding of Pakistan, this paper demonstrated the similarities and differences of religions’ roles in India and Pakistan. As a result, this paper found that religions were the ideological basis for both India and Pakistan to build a nation-state, but there are obvious differences in cohesion. Religious thoughts have influenced the national policies and administrative programs of the two countries in different degrees. Religions also more or less have strengthened the sense of national identity of each ethnic group in the two countries.