The most important and famous and adopted theory that is commonly held by the Orientalists about the sources of the Qur'an is the theory of adaptation of Qur'an based on Jewish and Christian sources, especially the two Testaments. According to this point of view, which denies the revelatory nature of the Qur'an and the prophethood of the Prophet of Islam (P. B. U. H. ), his holiness has learned many Jewish and Christian teachings through some Jewish and Christian groups and presented in the form of the Qur'an. These individuals and groups are considered by the Orientalists as the Prophet's instructors. This paper seeks to analyze this view fairly comprehensive, and defends the revelatory nature of the Qur'an, by reviewing and criticizing the challenges of Orientalists' points of view. Considering the Qur'an as a human work is the first problem, which is based on a wrong prejudice of the Orientalists. The second and more important problem is their unscientific method in dealing with the historical data. Following their assumptions, the historical data have emphasized and analyzed selectively, fanatically and unilaterally by the Orientalists. But lacking of such reports about the training of the Prophet (P. B. U. H. ) by others, non-continuing and limiting meetings of the Prophet (P. B. U. H. ) with the alleged instructors, giving glad tidings and confirming the Prophet (P. B. U. H. ), the conversion of some of them to Islam, the inconsistency of this story with the moral character of the Prophet (P. B. U. H. ), the critical approaches of the Qur'an towards the People of the Book, interrupting, delaying and waiting for revelation, the challenge of the Qur'an orTahaddi, emphasizing on the revelatory and supernaturally nature of the Qur'an and illiteracy of the Prophet are the other reasons that have been argued in the critique of Orientalist's theory.