Isma’ilis theory of Imamate is based on the their theory of sacred history. According to them, based on a pre-determined plan, history is divided into seven periods each of them begins with an Arch-prophet whose successors hermeneutically interpret the inner aspects of the religion of that period. The last period- which is the same as the period of the Qa’im of the Doomsday- will come to an end with the end of history. According to Isma’ilis, there are, in each period, a saying and a silent prophet and Imamate is for them the continuation of executorship. For Isma’ilis, Imamate is important since its links the earthy Imamate with the heavenly meanings (heavenly periods and worlds of intellects). Thus, Imam should be a descendant of the Holy Prophet (S) whose necessity of Imamate has been proved in the basis of rational and transmitted arguments and he should be appointed, Infallible and enjoy knowledge and superiority. One’s worships shall be accepted if he knows the Imam and his acts will be accepted if he obeys the Imam. In the Isma’ili thought, the end of history contains spiritual resurrection when the seventh saying prophet, as the Qa’im of the Doomsday, will describe the inner truths of the world; sometimes, this saying prophet is considered as the Promised Mahdi. Since some Mahdis have appeared among Isma’ilis, new interpretations have been introduced in this regard; and the seventh saying prophet (the Qa’im of the Doomsday) has been considered as an Imam who will take human beings to the highest station of spirituality.