This paper seeks to study the methodology of Ibn ×azm, a classical Andalusian Muslim theologian and jurist from the eleventh-century C.E. (Christ Era), in the field of comparative religion with special reference to his master piece entitled al-FaÎl fÊ al-Milal wa al-AhwÉ’ wa al-NiÍal - the Decisive Word on Sects, Heterodoxies, and Denominations. This study examines Ibn ×azm’s original contribution to the development of the science of comparative religion and discusses his methodology in dealing with theological doctrines of Christianity. The findings of this research will enrich the perspective of modern comparative religion with the insights of one of the most original Muslim treaties in theology and improve our understanding of contemporary Muslim approaches to the study and undertaking of comparative religious studies.