Credential is a document according to which the victory of a candidate in the elections is officially recognized and announced to the center. The MPs of the First Parliament or the National Assembly did not have the credentials. The first credentials were issued for the MPs in the Second National Assembly. The credentials were changed in form and content from tenure to tenure. In the early rounds of the National Assembly the credentials did not follow any rule or law in form and content. With the lapse of time and in the closing years of the National Assembly, the credentials became orderly and consistent. However, generally speaking, in all credentials the Board to Supervise Elections along with a state authority have introduced the MP belonging to their constituency and approved the elections’ conformity to the election rules and regulations. This paper intends to review the changes in form and content of the credentials issued during the past 24 rounds of the Islamic Consultative Assembly (Iranian Parliament) and compare and contrast these credentials in a descriptive way based on the documents, i.e. credentials.