Efficiency is the essence of an organization that can guarantee organizations' stability and survival and is a mechanism for gaining a competitive advantage. Leadership style is a set of attitudes, traits, and skills of managers formed based on the four factors of the value system, trust in employees, the leader's tendencies, and a sense of security in ambiguous situations. Therefore, the present research evaluates Audit firms' organizational Efficiency based on leadership styles (relationship-oriented and task-oriented) in 2019. The variables of organizational identity, individual effectiveness, and organizational commitment have also been used as mediating variables in the research. The present research method is the descriptive-survey type, and the statistical population is the managers of public and private sector Audit firms. Ahmadi Harisi Farahmand's (2015) standard questionnaire was used to measure organizational Efficiency, and a task-oriented and relationship-oriented leadership style questionnaire was used to measure leadership style. Data analysis is performed by the structural equation method using SPSS and PLS3 software. Findings show that a significant relationship between relationship-oriented leadership style and organizational Efficiency in the public sector with an acceptable significance coefficient is confirmed. However, it is rejected in private sector Audit firms. In contrast, the existence of a significant and negative relationship between task-oriented leadership style and organizational Efficiency in the private sector with an acceptable significance coefficient is confirmed. However, it is rejected in the public sector.