The first step in measuring the performance of a commercial unit is to calculate the efficiency achieved according to the goals set for it. Since the increase of shareholders' wealth has been proposed as the main goal of commercial units, therefore, a commercial unit should act in such a way as to increase the shareholders' wealth by obtaining appropriate returns. Therefore, the purpose of this research is to investigate the relationship between the auditor's tenure and the volatility of stock returns. The statistical population of the research companies admitted to the Tehran Stock Exchange and the studied sample includes 140 admitted companies during the years 2016 to 2016. The research method is descriptive and causal in terms of the relationship between the variables, and it is practical in terms of the goal. The regression method and panel data as well as the fixed effects model were used to process and test the hypotheses. The results obtained from the analysis of the hypotheses showed that the tenure of the auditor has a negative and significant relationship with the volatility of stock returns.