The purpose of this study is to examine the effect of leadership styles in auditing firms on auditors' professional competence, with an emphasis on the mediating role of behavioral entropy. Considering the importance of audit quality in enhancing public trust and reducing information risk, identifying factors influencing auditors' professional competence appears essential. This applied research was conducted using a descriptive-correlational method. The statistical population included 5,545 certified public accountants in Iran. The minimum sample size, based on Cochran’s formula, was determined to be 359; however, 489 individuals were selected through random sampling for the study. Data were collected using Hersey and Blanchard’s (1999) standardized situational leadership style questionnaire, along with researcher-made questionnaires on auditor professional competence and auditor behavioral entropy. Structural equation modeling was used to test the hypotheses. The findings revealed that the directive leadership style has a significant negative effect on auditors' professional competence, while the coaching and participative leadership styles have positive and significant effects. The delegative leadership style did not have a significant effect on professional competence. Additionally, results confirmed the mediating role of behavioral entropy: coaching and participative styles increased professional competence by reducing behavioral entropy, whereas the directive style negatively affected professional competence by increasing behavioral entropy. The findings emphasize the importance of selecting appropriate leadership styles in auditing firms and indicate that leaders employing participative and supportive approaches can foster the enhancement of professional ethics, behavioral cohesion, and audit service quality improvement.