Despite the increasing number of studies dealing with the history and culture of Sassanid Iran, there are but a few mentions of the process during which a Sassanid king was elected, so the question of succession under this dynasty has been overlooked. In historical accounts of those periods when the power of the central government of the Sassanid dynasty was at its height, the kings chose to elect their successors when they were still alive, while during the periods of decline, kings used to be elected through the intervention of the nobles, royal families, and a notable body of electors who gave member of the king’s family the right of accession. However in Letter of Tansar to Ghōšnasb, the questoin of the succession of Sassanid kings is reported differently from the records in other historical accounts. In Letter of Tansar, mowbedān mowbed (the high priest), dabīrbed (chief secretary), and spāhbed (general), have been called the electors of Sassanid kings. This study aims at finding an acceptable answer to the contradiction between the report of the Letter of Tanssar and other historical accounts, rather than calling this process of succession reflected in Letter of Tanssar as "faked."