The present study investigates the effect of cognitive diversity of auditors signing audit reports on audit quality. To achieve the research objective, financial information of 156 companies listed on the Tehran Stock Exchange during the period from the beginning of 2014 to the end of 2015 was used, and to test the research hypothesis, multiple regression and mixed data were used. This study shows that cognitive diversity (difference in expertise and experience) has a positive and significant effect on audit quality, while demographic diversity (gender, age) shows a negative or insignificant effect. The findings indicate that the benefits of team diversity in auditing are only realized when it is directly related to professional skills. Hierarchical structure and time pressures may also moderate the positive effects of diversity. The implications of these findings for the auditing profession and future research are very noteworthy. From a practical perspective, these results suggest that audit organizations should emphasize skill and expertise diversity in the formation of their teams, rather than focusing solely on appearance diversity.