The aim of this article is not so much to assess what Habermas and Rawls said about each other's work, as to examine how their respective theories deal with the important problem of the place and role of religion in public sphere. First of all, the author will clarify the intrinsic relationship between religious beliefs, the common will and public reason. Secondly, the author will explain the Rawls's attitude to religion or religious belief change is from exclusion principle to inclusive principle. Finally, the author will illustrate the methodological atheism in Habermas' view, and why he claimed that religion cannot be eliminated or replaced.