Objective: Today, identifying the factors affecting the credit rating is of particular importance in terms of comparing the credit risk of one firm with other firms and also in terms of competitiveness of the firm. The purpose of this study was the Investigating the Effect of Risk of Non-Repayment of Debts on Credit Rating Due to the Adjusting Role of Financial Constraints. Method: The present study is an applied research in terms of purpose. Also, in this study, according to the type of data and available analysis methods, the combined data method has been used. Data collection method, document mining method and referring to databases; and the method of data analysis is inferential. In the present study, the required data have been extracted from the new Rahvard software, corporate financial statements and documentation, as well as the Cadal site. The statistical population of the present study is all companies listed on the Tehran Stock Exchange in the period 2102 to 2120and the software used to prepare data and estimate models is Eviews 10. Combined data model was used to test the research hypotheses. Results: The results of the research hypotheses test show that companies that perform poorly in repaying the principal and interest of their financial obligations cause distrust of creditors, which in turn reduces the credit rating of the company. The results also showed that financial constraints have a positive effect on the relationship between the risk of non-repayment of debts and the credit rating of the company. Thus, companies with financial constraints have a high risk of non-repayment of debts, and as a result, the distrust of creditors increases, which leads to a decrease in the credit rating of companies. Conclusion: Investors and lenders like to pay more attention to companies with less financial constraints. As a result, these companies find greater credibility with investors and lenders through easy financing. Also, the increased risk of non-repayment of debts causes the creditors to be pessimistic about the company for not paying their financial obligations; As a result, in such a situation, easy and varied financing will have a significant impact on reducing the risk of non-repayment of debts and lenders will increase the credit rating of companies. Investors and creditors can use the results of this study to select the right companies to invest. Also, organizations that rank companies can use the risk of non-repayment of debts and financial constraints as two very important and determining factors in the ranking.