Chuvashes are the descendants of Idil-Bulgarians who had accepted Islam firstly as a state religion in Turkish history. Some of them have kept the traditional Turkish believes alive up to the present day. Today they have been regarded as a Christian Turkish community. Therefore Chuvashes have an exceptional place from the point of view of the history of religions and the history of Turkish culture in Turkish world. From the time Chuvashes began to accept Islam to the present, generally those who had been living in the rural area accepted Islam superficially. Thus Islam was not effective in their moral life. But afterwards among Chuvashes who accepted Islam were imams, muazzins, teachers in a madrasa and the other religious affairs. However many of them who accepted Islam, had been Tatarized through fusion with Tatars who were strong representatives of Islam in the Volga-Ural region. This caused Chuvashes to define themselves as Tatars. In the same time the Muslim Chuvashes have been registrated as Tatars in written sources. Chuvashes who had been continuing traditional religious believes were also influenced from the Islamic culture. This influence has been seen on their rites, religious practices and terminologies. In this article, the relation of Chuvashes with Islam and the alteration ethnicity of them by way of Tatarization have been studied throughout the history