Internal auditing is an independent, objective assurance and consulting activity that helps an organization accomplish its objectives by bringing a systematic, disciplined approach to evaluate and improve the effectiveness of risk management, control and governance processes. As the roles of internal auditors increasingly change in organizations, new competencies are needed. The purpose of this research is to Identify and prioritize competencies of internal audit managers. In this research, mixed methods (quantitative and qualitative methods) are used. In other words, first, qualitative research method and grounded theory approach are used for Identifying competencies. To achieve this goal, with obtaining 18 faculty members and internal auditing experts insights through unstructured interviews in 2018-2019, we developed internal auditors’ competency model in Iran. According to this model, internal auditor managers need a series of Individual, technical, managerial and environmental competencies to achieve the desired level of effectiveness. Then, in the quantitative part of the research, by analyzing the questionnaires received from internal auditors and using Friedman's test, we prioritized the dimensions of competence of internal audit managers in the small, medium and large companies of Iran. The research results show that three dimensions of work experience, academic education, and Mastery of Internal Audit Standards in small, medium and large Iranian companies have a higher priority than other dimensions. In addition, in large companies, intellectual and analytical competencies, expertise in risk management, governance, information technology and quality frameworks have a higher priority than small and medium companies, which can be due to complex operating cycles and processes.