This study investigated the effect of the audit firm's rating and its opinion on the relationship between financial statement restatement and profit smoothing in companies listed on the Tehran Stock Exchange. First, the relationship between financial statement restatement and profit smoothing was examined, and the results showed that this relationship is positive and significant. Next, the role of the audit firm's rating was examined, and it was determined that higher-rated firms have a negative and significant effect on profit smoothing. Also, accurate and independent auditors' opinions also lead to a decrease in profit smoothing. This study was conducted using a quantitative, descriptive, and retrospective research method, and data from 116 companies were analyzed during the years 1397 to 1401. The results showed that financial statement restatement leads to a decrease in companies' tendency to profit smoothing. In addition, the audit firm's rating and independent auditors' opinions improve the transparency and quality of financial reporting and reduce profit smoothing behaviors. The findings of this study highlight the importance of using reputable auditing firms and strengthening auditor independence. Also, monitoring the restatement of financial statements, reducing profit smoothing behaviors, and educating financial managers about its consequences are introduced as effective solutions. Finally, encouraging correct and ethical reporting and improving internal audit processes are emphasized to increase financial transparency and prevent profit smoothing.