This research is responsible for examining the letters of Imam Sadiq (AS), which number 67 letters. The mentioned letters were examined and analyzed from two perspectives. First, in terms of appearance, by examining the internal and external structure of the letters of Imam Sadiq (AS), an attempt was made to clarify the format of the Imam's letters and their differences or conformity with the customary letter writing form of the time of Imam Sadiq (AS). In examining the internal structure, topics such as the beginning and end of the letters, the sender and the way he is mentioned, the recipient and his position, the volume of the letter and internal citations were examined, and in examining the external structure, topics such as the number of letters, type of letter, destination of the letter, writing instrument, letter transmission system and the main carrier were examined. Second, the letters were examined from the content perspective. By analyzing the content of the Imam's letters and identifying the main and secondary topics of the letters and classifying them, the main concerns of the Imam and the Shiites were identified through examining the content of the letters. The main achievement of the research is that the structure and main form of the Imam's letters are not much different from other letters and the lack of uniformity in the Imam's letters is due to the shortcomings in the way the letters are transmitted in the texts because the narrators have selectively narrated the letters according to their tastes, but in terms of content, the emphasis on religious and jurisprudential instructions is among the characteristics of the letters of Imam Sadiq (peace be upon him), which has allocated a larger volume of letters. Considering the significant volume of the remaining letters from the Imam (67 letters), it can be guessed that the Imam's letters were more than this and this volume itself indicates the Imam's jurisprudential and religious authority in the Shiite