Ash'arism has been systematized with the conceptual and methodological contributions of scholars who followed Ebu'l-Hasan el-Eş'arî. Like Bakıllânî and Ibn Fûrek, Ebû Ishâk el-Isferâyînî had been accepted as one of the scholars who provided the systematization of this school in the early period. Cuveynî, Gazzâli and Râzî often refered to Ebû İshâk el-İsferâyînî and this indicated el-İsferâyînî's position within the sect. Therefore, el-Isferâyînî has a great influence to Ash'arite theologians in particular as a methodological. The most important feature of el-Isferâyînî is that he advocates the different opinion from general approach of sect. He, in some respects, has left general opinion of school and followed the thought of Maturidism and adopted some of Mu'tezile ideas. This article examines his contributions to the process of Ash'arism on the basis of his theological system. In this respect, his different opinions within sect will be discussed, especially will be focused on assesing his methodological approaches then trying to determine his influences on the later theologians.