This study aimed to describe the background of letter’s used as a medium for da'wah by the Prophet Muhammad and the form of the Prophet Muhammad’s letters for da'wah conveyed to some rulers. To achieve this, the method employed was historical research. This type of research was qualitative using historical approach while the research specification was descriptive. The result shows that there were several reasons behind the sending of letters as a medium for da’wah by Prophet Muhammad to the rulers. First, sociologically it was due to the treaty of Hudaibiyah, then the successfulness of Prophet Muhammad in establishing people power in Medina, and the conflict between Emperor Heraclius and Khosrow Abrawiz, two rulers of two empires (those wer...